B is the correct answer.
The logic is as follows:
To prove that the first statement is not sufficient try to pick a few number and you will see that the remained can be 0 and 1 (as with x=10&12 and y=3&4, respectively)
2) (x+y)/y (remaider 4) can be simplified to x/y + y/y. Since y/y never has a remainder, regardless of the value of y, the remainder when x is divided by y will always be the same as the remainder when (x+y)y