Damn, people be posting some tricky questions. This one is easy but it sucks because logically you need both. But you need to employ this general equation which I've seen in the GMAT before. Sales - expenses = gross profit. A states that GP = 1/3E. Plugging this into the equation gives you S - E = 1/3 E. Multiply both sides by three and get 3s-3e = e. Add 3e to both sides to get 3s=4e. This can be simplified to 3/4=e/s. so the ratio of expenses to sales is three to four. Plug this ratio into the equation and get 4-3=1. Therefore, A is sufficient because you can tell that the ratio is 1/4. Eliminate B,C,and E.
B says expenses were 3/4 revenue. This is saying e=3/4r. Following the same logic in one you can quickly tell that both of these are correct and that the answer is D. I don't like this only because it's tricky and it assumes you know the profit formula which isn't talked about much but can apparently show up. It's not a hard formula to remember and you should know it but just look out for tricky stuff like this.
