______ it have been the failure to pick up directions from the ground control that caused the air crash?
| A．Must | B．Could | C．Would | D．Should |
I remember sometimes in a rush to grow up and be independent， but I was still very happy.
| A．to feel | B．felt | C．being feeling | D．feeling |
Doctors have been researching effect stand-up and other forms of comedy have on us.
| A．which | B．what | C．whatever | D．whichever |
---- ________ you spoil everything, Kevin?
---- Please don’t get me wrong. I just want to help and I am a good man and I ….
| A．Must | B．May | C．Can | D．Will |
After 15 years in the USA, he finally decided to ________ American citizenship.
| A．concentrate on | B．apply for |
| C．put off | D．lead to |
Nowadays, China has become the largest consumer of mobile phones. _______, every person has one mobile phone.
| A．Above all | B．In other words | C．On the whole | D．On average |