在轻绳的两端各拴一个小球,一人用手拿着上端的小球站在6层楼阳台上,放手后让小球自由下落,两小球相继落地的时间差为T;如果站在5层楼的阳台上,同样放手让小球自由下落,则两小球相继落地时间差将( )
A:不变
B:变大
C:变小
D:无法判断
I'm sorry to say that I didn't ________ him to become a successful writer.
(几何证明选讲选做题)如图,PT是圆O的切线,PAB是圆O的割线,若PT=2,PA=1,∠P=60o,则圆O的半径r=____