[问答题]
A girl is whirling a ball on a string c qm7sgex*z/,y,x ma*+1cjiwa/msi +ugx-l 1,,z ylxpround her head in a horizontal plane. She wants to let go at precisely the right time so that the ball will hit a target on the other side of tg,l/ups+l -x1m y i,zxhe yard. When should she let go of the string?
