[问答题]
A girl is whirling a ball on a string around her head in a horiz*7ym/q( akb ikontal plakjov8s43vyc/ c1b+u une. She wants to let go at precisely the right time so that the ball will hit a os+b 4vuv3yjccu/k1 8target on the other side of the yard. When should she let go of the string?
