Question

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

1. A.
   For
2. B.
   As
3. C.
   Though
4. D.
   Unless

Answer 1

B
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。