问题补充:
Was it because of the heavy snowstorm in Europe the flight had to be put off?
A. which
B. so
C. why
D. that
答案:
A. which
B. so
C. why
D. that
解析:考察强调句型。It is/was被强调成分that/who其他成分;这是强调句型的基本结构。本题强调的是介词短语because of the heavy snowstorm in Europe。故D正确。