临床上出现舟状指甲、苍白，甲面变粗，有脊形纹症状，可能缺乏（）
A、锌
B、铁
C、维生素c
D、维生素a
参考答案：B
--- Hi Mike, are you busy now?
--- Not really. I _____ my work, and I’m going to see a movie online.
A．did
B．have been doing
C．had done
D．have done
