In order to find _____ better job, he decided to study ____ second foreign language.  

A．the; a

B．a; a

C．the; the

D．a; the

在通常情况下，空气中的声速是_______m/s，一个雷雨天，小芸从看到闪电到听到雷声大约经过3s，由此你估算打雷处到小芸的距离大约是____米。