When I try to understand __________that prevents so many Americans from being as happy as one might expect, it seems that there are two causes.
| A．why it does | B．what it does | C．what it is | D．why it is |
______ city in Zhejiang Province, located on the river’s upper reaches, is believed to be ______ source of the dead pigs.
| A．The; a | B．The; the | C．A; the | D．A; a |
—Can I use your phone?
—______.
| A．By any means | B．My pleasure | C．With pleasure | D．Feel free |
I was really busy these days, otherwise I _______ to your birthday party last night.
| A．came | B．did come | C．should have come | D．would have come |
The company is quite honest and guarantees the new product ______ be under warranty for three years.
| A．should | B．shall | C．will | D．can |
—Haven’t seen Lucy recently. What’s happened?
—Oh, it’s more than two months ______ she worked here.
| A．before | B．after | C．since | D．when |