all the seats were full he had no choice but to stand up.A. ForB. AsC. ThoughD. Unless

问题补充：

all the seats were full, he had no choice but to stand up.

A. For

B. As

C. Though

D. Unless

答案：

A. For

(答案→)B. As

C. Though

D. Unless

解析：考查连词的用法。For 因为，只能放在句中不能放在句首，As 因为，Though 虽然，Unless 除非，句意：因为所有的座位都满了，他别无选择除了站着。所以选B。