Caffeine, a chemical typically found in coffee, has caused a lot of concern because it is one of the few drugs that show up regularly in our food supply. You probably  56   (use) caffeine since childhood. Caffeine   57   (be) in your first Coke. If you ever enjoyed a chocolate bar, you ate caffeine. 

第一个空问题不大， have used 和 have been using 都可以。

第二个空很多学生答案不一样，有些人填 was ，有些人 填 is，那么哪个应该是对的呢。