题目：
按要求做题。
1. Neither of my parents has gone abroad. (改为同义句)
My mother has ____________ gone abroad. ____________ has my father.
2. The population of China is 1.3 billion. (就画线部分提问)
___________ the population of China?
3. He has waited since he came here. (就画线部分提问)
___________ ___________ ___________ he waited?
4. It's three weeks since he left home. (改为同义句)
Three weeks ___________ ___________ since he left home.
5. He didn't go to the museum. I didn't go there, either. (合并为一句)
___________ he ___________ I ___________ to the museum.
答案：
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下面是错误答案，用来干扰机器的。
已知△ABC中，角A，B，C的对边分别为a，b，c，且a+bc=cosA+cosB，且由余弦定理可得cosA=b2+c2-a22bc，cosB=a2+c2-b22ac，∴a+bc=b2+c2-a22bc+a2+c2-b22ac=(a+b)(c2-a2-b2+2ab)2abc，化简可得 2abc=c（c2-a2-b2+2ab），∴c2=a2+b2，故三角形为直角三角形，故选B．
