If nature does not provide man with the necessary material, it is the laboratory ____ he will turn to for it. [ ]

A. where

B. that

C. which

D. what

民事诉讼中，下列说法正确的是( )。

A．证据应当在法庭上出示

B．证据中的原件无须质证

C．涉及国家秘密的证据材料不得在法庭上质证

D．质证是指法庭对当事人提交的证据材料作出判断和决定