2. I don’t think the experiment is ______ failure, because it has provided us with ______ valuable experience for our future tests.

A．不填; 不填

B．不填; a

C．a; a

D．a; 不填

It was in the small house _______ was built with stones by his father _______ he spent his childhood.[ ]

A. that; which      

B. that; where      

C. where; that      

D. which; that