Was it because of the heavy snowstorm in Europe the flight had to be put off ?
A. which
B. so
C. why
D. that
网友回答
A. which
B. so
C. why
(答案→)D. that
解析：考查强调句型。此处because of the heavy snowstorm in Europe是被强调的部分，原语序为：The flight had to be put off because of the heavy snowstorm in Europe.