---Why were you late for school today?

----It was ________ I help catch a thief on the bus.

A．since

B．as

C．for

D．because

反映实验自变量与因变量的因果关系的真实性，决定实验结果解释的是( )。

A．内在效度

B．外在效度

C．生态效度

D．总体效度