Which sentence below shows correct use of em dashes?

in a thousand years, most of our greatest monuments-such as they are- will have crumbled to nothing

Explanation:

Em dashes can take the place of a comma, which is what would split up this sentence

the answer is b. the tracer looks harmless in flight, but the pilot’s bitten lips and white knuckles suggest how dangerous it can be.

sometimes we look at a photo and miss on important information because we don't know all the facts or don't have the complete story behind it. captions give viewers important and relevant information about the photo. most of the time we will look at the photo for a second time after reading the caption under the photo and then find something different or new about it. this visual trip is also known as a loop.

captions differ from descriptions because they're meant to be read by someone else while descriptions contain basic information that will anyone who is working with them.