血红蛋白M共发现几种（）
A.9种
B.6种
C.7种
D.5种
E.8种
参考答案：D
— Where is my pencil?
— ___________________[ ]
A. It's yellow.
B. It's on the floor.
C. It's so long.
钨极氩弧焊时，易爆物品距离焊接场所不得小于______。
A．5m
B．8m
C．10m
D．15m
