Complete each of the following sentences with a (compound) word derived from the one(s) given in brackets.
Since he is usually a cautious person, this sudden promise he has made regarding the investment is （ ）. (question)
【正确答案】：QUESTIONABLE
【题目解析】：
根据前文this sudden promise he has made regarding the investment is（对投资的突然承诺是······）可知应填question的形容词形式questionable，可疑的。
句意：由于他通常是一个谨慎的人，他对投资的突然承诺是可疑的。