sono sentaku wo koukaisite imasu.

その means that and points to something connected to the listener or something already mentioned in the conversation or text.

So その選択 means that choice or that decision.

This is part of the こ・そ・あ・ど series:

• この = this
• その = that
• あの = that over there
• どの = which

A learner may wonder why it is not あの. The difference is not just physical distance. その is often used for something already brought up or understood in context, so it fits naturally in sentences like this.

選択 means selection, choice, or sometimes option chosen. In this sentence, it refers to the choice that was made.

It is a noun, and it sounds a little more formal or abstract than some everyday English uses of choice. Depending on context, Japanese might also use words like:

• 決断 = decision, especially when emphasis is on making a judgment
• 選択 = choice/selection, focusing on the picked option

So その選択 is a natural way to say that choice.

を marks the direct object of the verb.

Here, the verb is 後悔しています, and the thing being regretted is その選択. So:

• その選択 = that choice
• を = marks it as the object
• 後悔しています = am regretting / regret

A useful point is that 後悔する behaves like a verb that can directly take an object with を, even though 後悔 itself is a noun.

It is originally a noun meaning regret, but in Japanese many nouns can combine with する to function as verbs.

So:

• 後悔 = regret
• 後悔する = to regret

In this sentence, the verb form is built from 後悔する:

• dictionary form: 後悔する
• -te form: 後悔して
• polite progressive/state form: 後悔しています

This noun + する pattern is very common in Japanese.

This is a very common question because -te iru does not always work like English -ing.

With many verbs, -te iru can show an ongoing action. But with verbs like 後悔する, it often shows a continuing state resulting from something.

So 後悔しています usually means:

• I regret it
• I am regretting it
• I have regrets about it

It suggests the regret is currently true now.

By contrast, 後悔します can sound more like:

• a habitual statement
• a future statement in the right context
• a less natural choice for talking about present emotional state

So for I regret that choice, 後悔しています is the natural form.

In practice, it often means a present state of regret: regret or am regretting.

Japanese -te iru does not match English tenses one-to-one. Here it usually expresses that the regret exists now, often as the result of an earlier action or decision.

So if someone made a choice in the past and still feels bad about it now, 後悔している is exactly what you would expect.

The difference is mainly about whether the regret is presented as current or as a completed past event.

• 後悔しています = I regret it / I am in a state of regretting it now
• 後悔しました = I regretted it

So:

• その選択を後悔しています。
  The regret is current.

• その選択を後悔しました。
  The regret is placed in the past. It may or may not still continue now.

For emotional states like this, -te iru is often the more natural choice when the feeling still applies.

Yes, absolutely.

その選択をしたことを後悔しています means regretting the act of having made that choice. It is more explicit.

Compare:

• その選択を後悔しています = regretting that choice
• その選択をしたことを後悔しています = regretting having made that choice

The shorter sentence is perfectly natural and common. The longer one adds extra clarity by turning the whole action into a noun phrase with こと.

Japanese often leaves out the subject when it is clear from context.

So even though English usually requires I, Japanese does not need to say 私は unless there is a reason to emphasize or clarify it.

That means:

• その選択を後悔しています。 = naturally understood as I regret that choice or they regret that choice, depending on context
• 私はその選択を後悔しています。 = explicitly I regret that choice

Japanese relies heavily on context, so omitted subjects are normal.

Yes. 後悔しています is polite because it uses います in the polite -masu style.

Compare:

• plain: 後悔している
• polite: 後悔しています

The sentence you were given is in a standard polite style, suitable for many normal conversations and writing situations.

It comes from 後悔する.

The verb する changes like this:

• する
• して in the -te form
• しています in polite -te iru form

So:

• 後悔する → 後悔して → 後悔しています

This same pattern appears with many suru verbs:

• 勉強する → 勉強しています
• 心配する → 心配しています
• 確認する → 確認しています

It is read:

その せんたく を こうかいして います。

Word by word:

• その = sono
• 選択 = sentaku
• を = o
• 後悔して = koukai shite
• います = imasu

A note for learners: the spaces are just there to make the sentence easier to read. Normal Japanese writing would usually be:

その選択を後悔しています。

Not always. Japanese has several words that can overlap with choice or decision, and the best one depends on context.

For example:

• 選択 = choice, selection
• 決断 = decision, often more serious or weighty
• 判断 = judgment
• 選んだもの = the thing chosen

So if the sentence is about picking one option from several, 選択 works very well. If it is about a major life decision, 決断 might sometimes be more natural.

Still, その選択を後悔しています is completely natural Japanese.

Yes. It can be used for both, though the tone may feel somewhat stronger or more formal than casual English regret in some contexts.

Examples:

• regretting not studying
• regretting a relationship choice
• regretting a life decision

For very casual situations, Japanese might also use other expressions depending on nuance, but 後悔する is the standard and very common verb for to regret.

So this sentence sounds natural whether the choice was minor or major, though the overall tone is a bit neutral and direct.