① How does the paper feel? ____     A. It's water.

② Do you like winter or summer?____     B. It's soft.

③ Taste it. Is it milk or water?____     C. I like winter.

④ How do the grapes taste?  ____     D. It's ice.

⑤ It feels hard and cold. What is it?____     E. They are sweet.

通常情况下，声音在空气中传播的速度约 ____m/s．某次打雷时，看到闪电后5s才听到雷声，由此可以估算出发生雷电处离你的距离为 ____　m．

汪康年在《论中国参用民权之利益》中道：“中国之言治者曰：以君治民而已。”这一现象结束于（    ）

乙炔（C₂H₂）是生产聚氯乙烯的重要原料．用电石（主要成分为CaC₂）与水反应可制取乙炔，最终还可得到电石渣．某电石渣中含氢氧化钙92.5%，其余为杂质，此电石渣可用于处理电镀厂排出的酸性废水．