[问答题]
A girl is whirling a ball on a string around (f ohu(t :(si ttal 4(.1eoznxipu. p3her head in a horizontal plan qfkl1oo3rv* /1 iop5me. She wants to let go ao5*r1i3qovkm/of 1 lpt precisely the right time so that the ball will hit a target on the other side of the yard. When should she let go of the string?
