Jack describe his father, who____ a brave boy many years ago, as a strong-willed man
A.would beB.would have beenC.must beD.must have been在线课程D
解析：
考查情态动词表推测。因为是对过去事实的推测，要用情态动词+完成时态，排除A,C；
根据as a strong-willed man.作为一个意志坚强的人，可知他许多年前肯定是一个勇敢的男孩。所以选D，表示肯定……。