—Could you tell me _______?      —He is in the library. [ ]

A. where Simon was

B. where is Simon

C. where was Simon

D. where Simon is

患儿，男，2岁，由父母亲陪同去口腔科就诊，母亲要求医生为小孩作乳牙窝沟封闭，医生认为该小孩目前不需作窝沟封闭，其主要原因是

A．乳牙不需作窝沟封闭

B．现阶段儿童不易患龋

C．封闭剂的氟释放，儿童易误吞造成氟中毒

D．乳牙窝沟封闭年龄一般应为3～ 4岁

E．乳牙有机质多，封闭剂易脱落