选D,因为后一半是定语从句.
如果选A,则前后应该是并列分句,分句中间就要加连词and.
请看这三个句子:
Johninvitedabout40peopletohiswedding,mostofwhomarefamilymembers.(后半句是定语从句,从句的主语是mostofwhom,谓语是are.)
Johninvitedabout40peopletohiswedding,andmostofthemarefamilymembers.(后半句是并列分句,分句的主语是mostofthem,谓语是are.)
Johninvitedabout40peopletohiswedding,mostthembeingfamilymembers.(后半句不是从句,也不是分句,只是一个现在分词短语.因为它没有谓语动词.)
逗号不能连接两个并列分句,并列分句之间即使有逗号,也还要相应的连词,如and,but,or。但主句和从句之间只有逗号就可以了。