问题补充：
“Not having returned home yet, ”, his father said to the police.
A. his mother got worried
B. his mother must be worried
C. I think he is missing
D. he must have got into some trouble.
答案：
A. his mother got worried
B. his mother must be worried
C. I think he is missing
(答案→)D. he must have got into some trouble.
解析：句意：他的父亲对警察说：“还没回到家呢，他一定陷入了困境当中。must have done表示对过去事情肯定的推测。所以选D。
