Well, whoever gave you this test knows nothing. Unless these sentences are taken from context. #3...all four are possible!!!!! #2...a #1...a or d "d" is the obvious choice, and "a" would sound a bit cynical.

1) "A hardworking man may not become a great scientist, but a great scientist must be a hardworking man." Here "may not" indicates a possibility. "Must" indicates a strong obligation. To write it another way, "Although a hardworking man doesn't always become a great scientist, it is very important that a great scientist be hardworking." "Can" doesn't fit here because that suggests that you can also be a great scientist either through luck, or in spite of your laziness. 2) "No one enjoys being laughed at." "To enjoy" needs a thing as its object, so the verb must be in gerund (+ing) form. "No one enjoys laughing at" is an unfinished sentence. By using the passive voice (to be laughed at), you've already indicated the target of the laughter: the person in question. 3) "When I saw them last time,they were working on the farm." This is my first pick, but Eliot is right: all four are possible. "At" suggests they might also work somewhere else. "In" is the least likely possibility, but it means within the area of the farm, ie. within the farm's boundaries. "By" indicates "next to".

A hardworking man" may not "become a great scientist, but a great scientist " can " be a hardworking man No one enjoys " being" laughed at When I saw them last time ,they were working " on " the farm

d c d 吧。。。个人意见 仅供参考 不对不怪我！！

D, C & D. I'm unsure of the particular rules of grammar, but I've been a native speaker of English for over half a century. The first question is also logic. The harworking man can become a great scientist - but might not - so the choice is reduced to B or D. I doubt a person can be lazy and also be a great scientist, so my guess is D.