半数致死量（LD50）
参考答案：是指引起一半实验动物死亡的剂量。
A．George always tells the truth.
B． George lives too far to visit us.
C．It is kind of George to assist me in the filling station.
D．It is worthwhile to make friends with George.
车种代号W是（）。
A.长大货物车
B.毒品车
C.粮食车
D.通风车
