Smoking is a very bad habit, which many people find difficult to().

单项选择题As there was a power cut in the hospital, the surgeon had to () the operation.

A. call for
B. call on
C. call off
D. call up

单项选择题When the manager went to Canada on business, his () took over all his duties.

A. caretaker
B. officer
C. deputy
D. commander