Lawrence Craven, a doctor from the USA, is the author of several published reports, one of ________ 

 introduced the idea in 1953 ________ aspirin could reduce the risk of heart attacks.[ ]

A. them; when        

B. which; that

C. what; that          

D. which; when

裂解汽油加氢装置一段催化剂活化完毕后才能引入氢气。