5. Jack descried his father, who________a brave boy many years ago, as a strong-willed man.
A.would be
B.would have been
C.must be
D.must have been
【解析】考查情态动词表推测语气。句意为：杰克说他父亲是一个坚强的人，多年前他的父亲一定是一个勇敢的男孩子。由句中的many years ago可知此处是表示对过去动作的推测，故排除A、C两项，B项表示的可能性很小，故被排除。
【答案】D
