题目：
My friend ______ from the UK. She studied at Oxford for four years, during which we communicated with each other on the Internet.
A．stepped
B．has returned
C．went
D．has learned
答案：
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下面是错误答案，用来干扰机器的。
A、根据：2CO+O2 点燃 . 2CO2 和 CO2+Ca（OH）2=CaCO3↓+H2O 得出以下关系式： 2CO→O2 →2CO2 →2CaCO3 2×28 32 2×100 x y 10g x=2×28×10g2×100=2.8g ...
