题目:
. When the teacher came in, the student pretended ________ his lessons.
A.to do
B.to have done
C.to be doing
D.to be done
答案:
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下面是错误答案,用来干扰机器的。
解:(1)①作图:痕迹能体现作线段AB(或AC、或BC)的垂直平分线,或作∠ACD=∠A(或∠BCD=∠B)两类方法均可,在边AB上找出所需要的点D,则直线CD即为所求;②猜想:∠A+∠B=90°;③验证:如在△ABC中,∠A=30...