[问答题]
A girl is whirling a ball on a string arouym89wgvbebolea3 r :qt j-.76nd her head in a htljvg 3l oyi l64z9cc9;zk).lorizontal plane. She wants to let go at precisely the right time so that the ball will hit a target on the other side of the yard. When )icz6o 4.9 9 c vylkjlllgtz;3should she let go of the string?
