问题
选择题
Depression is the leading cause of suicide, __ __ in turn is the third leading cause of death among 15 to 24 year olds in the United States．
A．who
B．which
C．that
D．what
答案
答案：B
考查定语从句。句中which引导非限定性定语从句，指代前面的一件事，故选B。