I was astonished . . . . . . . . the sad news. A. to B. with C. at D. in

The correct answer is: C. at

The word “astonished” means “to be surprised or amazed.” In this sentence, the speaker is surprised and amazed by the sad news. The preposition “at” is used to express surprise or amazement.

The other options are incorrect because they do not express surprise or amazement. The preposition “to” is used to express motion towards something. The preposition “with” is used to express possession or association. The preposition “in” is used to express location or position.

Here are some examples of how the preposition “at” is used to express surprise or amazement:

• I was astonished at the news.
• She was astonished at the sight of the accident.
• They were astonished at the size of the house.