Rasha Assem posted:
……….passing the driving test is a must, you have to train well for the test.
a In case b Unless c As long as d Should
I think that 'c' is the answer and that 'a' is not correct. Am I right?
Yes, you are right on both counts: (c) is the answer and (a) is incorrect.
In speaking of what the addressee has to do, the sentence is talking about a necessity. Thus, it must be known to the speaker that passing the driving test is a must. Given that he knows that it is a must, he would not use "in case," which has conditional meaning. "As long as" is the only answer that makes sense.
As for the other two choices, (d) is ungrammatical and (b) is absurd.