D. they say means a group refer to as they, thinks or says that persuading her to join is a waste of time.

for correct grammar you would have to say we should choose those people with good character to be our friends. We should choose those people with a good character as our friends, is another grammatically correct way to say pretty much the same thing.

if someone asks you if you used to go to the Theater, it would be referring to a question asking if you went to the theater in the past. This generally implies that you wouldn't go to the theater often in the present or future.

off in an American English Stillwater is referring to natural water, like a pond porn stream, that has no movement and allows growth for algae and other plant life and a breeding spot for insects. In this context it's referring to water that is not carbonated or sparkling. In the United States still water in this context is simply refer to as water and carbonated water would be referred to as sparkling or carbonated water off some other kind of sort.

an anniversary band usually refers to a ring that has no setting for for a stone as in a diamond. An anniversary ring can be simply a band or the most extravagant and beautiful ring with giant stones on it. Try searching for images of male wedding bands. the anniversary differentiate from culture to culture as far as specific to the ring itself. as in, what kind of metal it is made of, or what kind of stones my included.

quiet literally means not loud. When referring to a person being quiet that usually means they don't speak often. This is not necessarily a bad or good trait.