humor是名词而不是形容词,楼上的错了,应该是
He must be very humorous.或者He must havea good sense of humor.他一定很幽默.
Can't he be humorous?他不可能幽默?
Could he have a sense of humor?他可能幽默吗?
(He could sense of humor?是陈述句语序而不是问句,而且情态动词后不能直接加名词的sense of humor,要加have）所以错了