—I called you at 9 last night，but no one answered.
—Sorry，I sleeping.I went to bed very early.
A. need have been
B. would have been
C. must have been
D. should have been
网友回答
A. need have been
B. would have been
C. must have been
D. should have been
解析：C
解析 根据答语中的“I went to bed very early”可知，此处为肯定推测，用must，表示问话人打电话时，答话人一定正在睡觉。must have done表示过去肯定做了某事。