Yesterday I was about to leave for the market my boss called and asked me to go
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Yesterday I was about to leave for the market ________ my boss called and asked me to go back to the office at once．
A.when
B.while
C.as
D.because
试题答案
A
解析：…be about to do sth when…固定句型，表示“……正要……此时……”。