A吧
all ,both,表示“都”,“全部”.
(1) both指两个人或物,而all指三个以上的人或物,在句中都可作主语、宾语、表语、同位语或定语.
Both of us want to go.我们两人都想去.
All of us should work hard.我们都应努力工作.
所以C和D不对.
1.Both are中both是代词pron.作主语.eg:There are two men over there,both are from America.=There are two men over there,both of them are from America.
2.are both中both是形容词adj.作主语同位语.eg:The two men over there are both from America."both"作主语同位语时,其位置在be动词,情态动词,助动词之后,实意动词之前.
所以A吧