القطة تختبئ خلف حاملة القطط.

Because the subject القطة is grammatically feminine singular.

In the present tense, Arabic verbs change to match the subject. For she/it feminine singular, the verb often begins with تـ.

So:

• هي تختبئ = she/it hides
• القطة تختبئ = the cat hides / is hiding

Here القطة is treated as feminine singular, so تختبئ is the correct form.

The dictionary form is اختبأ.

That is the past tense / citation form meaning to hide or to hide oneself.

A few useful forms:

• اختبأ = he hid / hid himself
• يختبئ = he hides / is hiding
• تختبئ = she hides / is hiding

So in this sentence, تختبئ means is hiding or hides, depending on context.

It is pronounced approximately takhtabiʾu in fully vocalized MSA.

A breakdown:

• تخ = takh
• تب = tabi
• ئ = a final hamza sound, like a brief catch in the throat

So: تَخْتَبِئُ

The hamza at the end is important. It is not just takhtabi; it ends with a glottal stop: takhtabiʾ.

In normal pausal pronunciation, the final case vowel may be dropped, so you may hear something closer to takhtabiʾ.

قطة is the normal everyday word for cat, and it is grammatically feminine.

That does not always mean the speaker is emphasizing that the cat is biologically female. In many contexts, it simply means a cat.

So in a learner’s mind, it is often best to think:

• قطة = cat
• and it behaves grammatically as a feminine singular noun

That is why the verb is feminine: القطة تختبئ.

خلف means behind.

In Arabic, words like خلف often behave like nouns of location or preposition-like words. They are commonly followed by another noun in a genitive relationship.

So:

• خلف حاملة القطط = behind the cat carrier

In fully vocalized Arabic, this would be:

• خلفَ حاملةِ القططِ

Here:

• خلفَ is a word of location
• حاملةِ is connected to it and is in the genitive
• القططِ is also genitive because it is the second part of another iḍāfa construction

Because حاملة القطط is an iḍāfa construction.

In Arabic iḍāfa:

• the first noun usually does not take الـ
• the whole phrase becomes definite if the second noun is definite

So:

• حاملة قطط = a cat carrier / carrier of cats
• حاملة القطط = the cat carrier / carrier of the cats

Even though حاملة has no الـ, the whole phrase can still be definite because القطط is definite.

This is very common in Arabic.

Because Arabic often expresses this kind of compound as carrier of cats, using a plural noun.

So:

• حاملة القطط = cat carrier literally carrier of cats

Using the plural here sounds natural because it names the type of object.

If you said something like حاملة القطة, that would sound more like the carrier of the cat or a carrier for one specific cat, depending on context.

So the plural القطط is the normal choice for the general object name.

These two words look very similar, but they are different:

• القطة = the cat
  Pronounced roughly: al-qiṭṭa

• القطط = the cats
  Pronounced roughly: al-qiṭaṭ

So:

• قطة has ـة at the end and is singular
• قطط is the plural

Also notice:

• قطة has a doubled ṭ sound: qiṭṭa
• قطط is pronounced with two ṭ consonants separated by a vowel: qiṭaṭ

That plural can be a little tricky at first.

Yes, absolutely.

Both are possible:

• القطة تختبئ خلف حاملة القطط
• تختبئ القطة خلف حاملة القطط

The difference is mainly one of word order and emphasis.

• القطة تختبئ... puts the topic the cat first
• تختبئ القطة... starts with the action is hiding

Both are normal in MSA. The sentence you were given is perfectly natural.

Because Arabic does not use a separate present-tense verb to be the way English does.

In this sentence, the main verb is already تختبئ = hides / is hiding.

So Arabic simply says:

• القطة تختبئ = the cat is hiding

There is no need for a separate word meaning is.

A fully vocalized version would be:

القِطَّةُ تَخْتَبِئُ خَلْفَ حَامِلَةِ القِطَطِ

The endings are:

• القطةُ — nominative, because it is the subject
• تختبئُ — present-tense indicative ending
• خلفَ — accusative as a ظرف / adverbial of place
• حاملةِ — genitive after خلف
• القططِ — genitive as the second part of the iḍāfa

In normal everyday unvowelled writing, these case endings are not shown, which is why the sentence appears simply as:

القطة تختبئ خلف حاملة القطط.