Synonyms for quit

[Sultano]

Hello,
Concerning English Synonyms Tests,Synonyms for quit. I have some confusing words.
could you set me forth the difference between "abandon" and desert?
1- in this sentence: Unloyal sailors often.....their ship.
a) abandon b)desert
My answer is : abandon because we can say abandon the ship which it means the ship is sinking and here in this sentence it refers to that. , but in the key answer it is : desert . why? I get confused.

And here is another sentence:
2- He easily left .....his career.
a) left b) abandoned
My answer is : left , but in the key answer is: abandoned... Could you tell me why?

3-The teacher asked the students to .........talking.
a) give up b)quit
My answer is : give up - but in the key answer is : quit
Doesn't "give up " mean "stop" ?
We can say " He gave up smoking. " - or "He quitted smoking." and if give up means stop doing habits ,I think in that sentence" the teacher asked the students to .....talking,it's a custom and students always talk in the class..could you show me the difference?
I would be grateful.