— We should wait ______ others are breaking the rule.
A:if
B:unless
C:although
D:because
①城濮之战 ②“围魏救赵” ③长平之战 ④即墨之战
如图,在直角三角形ABC中,∠ACB=90°,D是AB上一点,且∠ACD=∠B.
求证:CD⊥AB.