zhèxiē èrshǒu wánjù kěyǐ zàilìyòng.

这些 means these and refers to more than one thing.

• 这 = this
• 这些 = these

So in 这些二手玩具, 这些 points to a plural noun, 玩具.

A very similar pattern is:

• 这个玩具 = this toy
• 这些玩具 = these toys

That is normal. 些 already functions as a plural-type word, so you do not add a measure word after 这些.

So you say:

• 这些玩具 = these toys

not normally:

• 这些个玩具 in standard careful Mandarin

Compare:

• 这三个玩具 = these three toys
• 这些玩具 = these toys

In other words:

• 这 + measure word + noun is used when you specify the number or unit
• 这些 + noun is used for an unspecified plural group

Literally, 二 means two/second and 手 means hand, so 二手 literally means second-hand.

In everyday Chinese, 二手 is the normal word for things that have been owned or used before, such as:

• 二手车 = a used car
• 二手书 = a second-hand book
• 二手玩具 = second-hand toys

It works very much like English second-hand or used.

Because 二手 directly modifies 玩具 as a close noun modifier, and in this kind of common expression, 的 is usually omitted.

So:

• 二手玩具 = second-hand toys

is more natural than:

• 二手的玩具

Both can be understood, but 二手玩具 sounds more compact and more like a normal noun phrase.

A good rule of thumb: when the modifier and noun form a common, tight combination, Chinese often leaves out 的.

Here 可以 means something like can, may, or is able to, but the best interpretation in this sentence is possibility/suitability:

• 这些二手玩具可以再利用。
• These second-hand toys can be reused / are reusable.

It does not mainly mean permission here.

Compare:

• 你可以进去。 = You may go in. → permission
• 这个办法可以。 = This method works. → acceptable/feasible
• 这些玩具可以再利用。 = These toys can be reused. → possibility/suitability

You can understand it both ways, but for learners it is very useful to see the structure as:

• 再 = again
• 利用 = make use of / utilize

So 再利用 means use again or reuse.

In modern Chinese, 再利用 is also commonly treated as a set expression meaning reuse or recycle for further use, so you will often encounter it almost like a vocabulary item of its own.

This is a very common question.

Both 再 and 又 can relate to repetition, but they are used differently:

• 再 is usually for something that happens again later, or for a repeated action that is still possible or intended
• 又 is usually for something that has already happened again

In this sentence, the toys can be used again, so 再 is the natural choice:

• 可以再利用 = can be used again / can be reused

If you used 又, it would sound like the action had already happened again, which does not fit as well here.

Because Chinese normally puts modal verbs like 可以 before the main verb phrase.

Structure:

• subject + 可以 + verb phrase

Here:

• 这些二手玩具 = subject
• 可以 = modal verb
• 再利用 = main verb phrase

So:

• 这些二手玩具可以再利用。

is the natural order.

Also, 再 comes before the verb it modifies:

• 再利用 = use again

So the overall pattern is very regular: subject + modal + adverb + verb

Not exactly. They are related, but not identical.

• 再利用 = reuse / put to use again
• 重复使用 = use repeatedly / use again
• 回收 = recycle / recover / collect for recycling

Differences:

1. 再利用 often focuses on giving something a new or continued use.
2. 重复使用 focuses more directly on using the same thing again.
3. 回收 often refers to collecting materials or items so they can be processed or recycled.

So for toys, 可以再利用 sounds very natural if you mean they do not need to be thrown away and can still serve a purpose.

Yes, you could.

The difference is mainly structural:

• 这些二手玩具 = these second-hand toys
  
  • 二手 directly modifies 玩具
• 这些玩具是二手的 = these toys are second-hand
  
  • this is a full sentence with 是

So the original sentence treats 二手 as part of the noun phrase:

• 这些二手玩具可以再利用。

But if you want to emphasize the condition of the toys, you could say:

• 这些玩具是二手的，也可以再利用。

Both are natural; they just package the information differently.

A careful pronunciation is:

• 这些 — zhèxiē
• 二手 — èrshǒu
• 玩具 — wánjù
• 可以 — kěyǐ
• 再利用 — zàilìyòng

Full sentence:

• zhèxiē èrshǒu wánjù kěyǐ zàilìyòng

A few pronunciation notes:

• 这 is fourth tone: zhè
• 些 is first tone: xiē
• 二 is fourth tone here: èr
• 手 is third tone: shǒu
• 玩具 is wánjù, with 具 in the fourth tone
• 可以 is kěyǐ, both third tones in citation form
• 再 is fourth tone: zài

In natural speech, the sentence flows smoothly without any unusual tone changes that beginners especially need to worry about.