He can swim very well and very ____.

医用“B”超机是利用超声波来诊断病情的，但人们听不到它发出的声音，这是因为（　　）

2005年10月12日,我国"神舟"六号载人飞船成功发射,航天飞船是用铝粉与高氯酸铵的混合物的固体燃料,点燃时铝粉氧化放热引发高氯酸铵反应:2NH₄ClO₄==N₂+4H₂O+X+2O₂,则X的化学式为       （）

节日里，为表达我们对妈妈的祝愿，我们可以给妈妈制作____。

Fanny and Benny live in the ____ estate. They go to school ____ every morning. They are good friends. But they have ____ hobbies. Fanny usually reads books at home in his spare time, and Benny likes bicycling.