Lawrence Craven, a doctor from the USA,
题型：选择题
问题：
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
是正定的，则t的取值范围是______.