zuówǎn wǎngluò bù wěndìng.

In Mandarin, time words often come near the beginning of the sentence, before the thing being talked about.

So:

• 昨晚 网络 不 稳定。
• literally: Last night, the network was not stable.

This is very natural Chinese word order.
English often puts the time expression at the end, but Chinese very often places it earlier.

A common pattern is:

Time + topic/subject + comment

So here:

• 昨晚 = last night
• 网络 = network / internet connection
• 不稳定 = not stable / unstable

They are very close in meaning.

• 昨晚 = last night
• 昨天晚上 = yesterday evening / last night

昨晚 is shorter and very common in everyday speech.
昨天晚上 is a little fuller and slightly more explicit.

In this sentence, both work:

• 昨晚网络不稳定。
• 昨天晚上网络不稳定。

Both are natural.

网络 literally means network. In everyday use, it often refers to:

• the internet
• the network connection
• the data network
• Wi‑Fi / online connectivity, depending on context

So in this sentence, 网络不稳定 usually means something like:

• the internet was unstable
• the connection was unstable
• the network was unreliable

The exact English wording depends on the situation.

Mandarin usually does not need a word equivalent to English was in this kind of sentence.

In English, we say:

• The network was unstable.

In Mandarin, adjectives can often function directly as the predicate:

• 网络不稳定。

So Chinese does not need a linking verb like was here.

This is a very important pattern:

• 天气很冷。 = The weather is cold.
• 他很忙。 = He is busy.
• 网络不稳定。 = The network is unstable.

Because 是 is generally not used before an adjective predicate.

You use 是 mainly when linking one noun to another, like:

• 他是老师。 = He is a teacher.

But with adjectives such as 稳定, Chinese normally does not say:

• 网络是不稳定。 ❌

Instead, it says:

• 网络不稳定。 ✅

So:

• noun + adjective → usually no 是
• noun + noun → often 是

It is often called an adjective in learner-friendly explanations, but in Chinese grammar it behaves a lot like a stative verb.

That is why it can directly serve as the predicate of a sentence:

• 网络稳定。 = The network is stable.
• 网络不稳定。 = The network is not stable.

So if you are thinking in English, it helps to treat 稳定 as stable, but remember that Chinese adjectives can act more like verbs than English adjectives do.

Chinese often forms negatives very simply by putting 不 before an adjective or verb.

So:

• 稳定 = stable
• 不稳定 = not stable / unstable

Both English translations are fine.
Even if English prefers a single word like unstable, Chinese commonly just says 不 + adjective.

In writing, it is still 不 and the pinyin is usually written bù.
But in actual pronunciation, 不 changes tone before another fourth-tone syllable.

Since 稳 in 稳定 is fourth tone (wěn is actually third tone—wait, important point: the first syllable of 稳定 is wěn, third tone, not fourth), there is no tone change here.

So in this sentence, 不稳定 is pronounced:

• bù wěndìng

not bú wěndìng

A useful rule:

• 不 becomes bú only before a fourth-tone syllable
• otherwise it stays bù

Examples:

• 不好 → bù hǎo
• 不忙 → bù máng
• 不是 → bú shì

So here: 不稳定 → bù wěndìng

Chinese often omits information that is clear from context.

So 昨晚网络不稳定。 can stand alone if the listener already knows which network is being discussed. Depending on context, it could mean:

• the internet was unstable last night
• our network was unstable last night
• the connection was unstable last night

If you want to be more specific, you can add a subject or modifier:

• 昨晚我家的网络不稳定。 = Our home internet was unstable last night.
• 昨晚公司的网络不稳定。 = The company’s network was unstable last night.

Yes. That means:

• The network was very unstable last night.

Compare:

• 网络不稳定。 = The network was not stable / was unstable.
• 网络很不稳定。 = The network was very unstable.

The sentence you were given is neutral and simple. Adding 很 makes the instability stronger.

Because this sentence is negative.

In affirmative sentences, Mandarin often uses 很 before an adjective:

• 网络很稳定。 = The network is stable.

This does not always mean very strongly; sometimes it just helps the sentence sound natural.

But in negative sentences, 不 already fills that role, so 很 is not needed:

• 网络不稳定。 ✅
• 网络很不稳定。 ✅ if you want to mean very unstable
• 网络很稳定。 ✅

So:

• affirmative adjective → often 很
• negative adjective → usually just 不

Yes, that can be understood, but 昨晚网络不稳定 is more natural and more common.

Chinese usually places the time expression before the subject/topic or right after it, but the sentence-initial time phrase is especially common.

Compare:

• 昨晚网络不稳定。 ✅ very natural
• 网络昨晚不稳定。 ✅ possible, but less standard/basic for learners

For a learner, it is safest to use:

Time + subject + predicate

Yes, absolutely. It is a complete and natural Mandarin sentence.

Chinese often allows short, efficient sentences when the context is clear. This sentence has everything it needs:

• 昨晚 = time
• 网络 = topic/subject
• 不稳定 = comment/predicate

That is enough to form a full sentence.

The tones are:

• 昨 = 2nd tone → zuó
• 晚 = 3rd tone → wǎn
• 网 = 3rd tone → wǎng
• 络 = 4th tone → luò
• 不 = 4th tone → bù
• 稳 = 3rd tone → wěn
• 定 = 4th tone → dìng

So in pinyin:

zuówǎn wǎngluò bù wěndìng

When speaking naturally, the third tones may sound a little different in connected speech, but the dictionary tones are as listed above.