A:must
B:shall
C:need
D:ca
(1)说出定理“线段垂直平分线上的点到线段两端的距离相等”的逆命题并证明这个逆命题是真命题.
(2)求证:三角形三条边的垂直平分线相交于一点.
—It's too late. Go to bed quickly.
—No,I won't go to bed until my work____.