如图,在△ABC中,∠BAC=90°,AD⊥BC于D,BD=3,CD=12,则AD的长为____
①该条件下H2的平衡转化率;
②用NH3表示0﹣2min内化学反应速率.
朱德“草堂留后世,诗圣著千秋”的对联中,“诗圣”指的是( )
-- Have you ever been to Paris, one of cities in Europe?
-- No. But one day I might go there on vacation.