The answer is not D or A. Probably B, Compare and contrast.
Answer:
Heart of stone
Explanation:
The saying "Heart of stone" is a figure of speech, you can't actually have a heart made of stone.
Well, it depends on what you're looking for but .gov and .edu websites are credible.
.org websites can be of good use too, but not all of them are credible
Vintage and old!! could mean from the olden days but also old seems a little less light