当空气中的甲烷含量增加到（）时,则氧的含量相对减少,会使人感到氧气不足,此时窒息现象是虚弱眩晕,进而可能失去知觉,直至死亡.

A.10%

B.1%

C.5%

D.0.1%

We know ______ about the new teacher except that she just came back from the US. We hope to know her better.

A．everything

B．nothing

C．something

D．anything