（）是指金属材料抵抗冲击而不致断裂的能力。
A.硬度
B.强度
C.塑性
D.韧性
参考答案：B
To everyone's surprise , Alex __________ play chess very well when he was only four. [ ]
A. might
B. should
C. would、
D. could
有效磷
