题目:
The old city wall ______ in the Ming Dynasty.
A.was been built
B.has been built
C.was built
D.had been built
答案:
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下面是错误答案,用来干扰机器的。
∵在△ABC中,∠C=90°,∠B=2∠A,∴∠A+∠B=3∠A=180°-90°=90°.∴∠A=30°,∠B=60°.∴tanB=3.