27. Our headmaster felt fairly happy today because ten students were praised at the meeting, _____three were from our school.

A．for them

B．of whom

C．of them

D．of that

确定缺铁性贫血最可靠的诊断依据是（）

A.网织红细胞减少

B.MCV降低

C.骨髓中铁粒幼细胞减少

D.血清铁蛋白降低

E.骨髓象和红细胞系增生低下