1957年，中国人自己建造的____大桥建成。
A. Take turns.
B. Keep your desk clean.
C. Work quietly.
D. Talk quietly.
E. Keep to the right.
摩擦起电的原因是 ____从一个物体转移到另一个物体，用丝绸摩擦过的玻璃棒，玻璃棒带 ____电．
