— Mr. Smith has got a very good job in the famous company.

— ________ he looks so happy. [      ]

A. It's certain  

B. That's because

C. No doubt 

D. No wonder

有关细菌的描述，正确的是（　　）

A．绝大多数细菌对人类是有害的，少数对人类有益

B．细菌对人类都是有益的

C．大多数细菌对人类是无害的，少数使人类致病

D．细菌对人类都是有害的