It is proved that John is really not so good at the job. He needs ___ by someone who

It is proved that John is really not so good at the job. He needs ___ by someone who

D。被可胜任的人替换掉
A 现在分词。后面不能跟by
B 动词原形，两个实意动词不能连续出现。
C need作为实意动词，need to do sth or need sth
作为情态动词，need do sth 。但是这里need 如果是情态动词，应该是原形。
D 作为实意动词，need必须根据三单规则，加s。