____千克
-- Judy's never been late for school, she?
-- . She is always the first to get to school every morning.
我国最早出现的国家是( )
掌握化学用语是学好化学的基础.请用化学用语填空:
(1)单质铁____ ;
(2)3个碳原子____ ;
(3)5个水分子____ ;
(4)硫在空气中燃烧____ .