单项选择题
After 15 years in the United States, he has finally decided to （） American citizenship.
A．concentrate on B．apply for C．look out for D．appeal on
单项选择题 How many more decades will have to pass （） scientists succeed in providing a cure for cancer？
单项选择题 The disease beri-beri （）．
单项选择题 According to the author, many teenagers think they are brave enough to act on their own, but in fact most of them （）．
