已知⊙O的半径为10,P为⊙O内一点,且OP=6,则过P点,且长度为整数的弦有( )
A:5条
B:6条
C:8条
D:10条
用光照射某种金属时,从该金属逸出的光电子的最大初动能随入射光频率的变化图线如图所示,普朗克常量h=6.63×10﹣34 J•s,由图可知( )
To everyone's surprise , Alex _____ play chess very much when he was only four .