What upsets him?—–_____ his computer is out of order．

___ the safety of gas, the government has checked the city’s gas supply system thoroughly. [ ]

I live far away from the school and I often _____ a bus to school. What about you— I go to school ________. It usually takes me about ten minutes.

It is uncertain side effect the medicine will bring about, although about two thousand patients have taken it

Guess what! I haven’t used this pen for ages and it ______.