Great changes __________ in China since 1980.a.has taken placeb.have been taken placec.took placed.have taken place

The correct answer is d. "have taken place".

Here's why:

The sentence is talking about multiple changes that happened in the past but have an effect on the present situation. In English, when we talk about an action that happened at an unspecified time before now, we use the present perfect tense.

The present perfect tense is formed with "has/have + past participle". The past participle of "take" is "taken".

So, we need to use "have" (because "changes" is plural) + "taken place".

Therefore, the sentence should read: "Great changes have taken place in China since 1980."