javascript - Questions about ajax?

Question

I accidentally encountered an ajax problem today. I have a question
Like the title

In option A, it is obviously wrong. Ajax itself cannot be accessed across domains.
In option B, I don’t understand it very well for the moment. Let’s leave it aside.
In option C, although ajax transmits data asynchronously, it can be synchronous as long as the third parameter of open is set to false.
D option Generally speaking, send is used to send data. If it is a get request, you can use open to directly attach the data to the url to have the effect of sending data.
Mainly because the answer to this question is C, I suspect the answer mistaken. The above is my understanding.

Answer 1

What are the requirements for this question=. =