⑴Did you learn languages ?____ A、It's my brother .
⑵Who's this ?____ B、Yes , he was .
⑶What is she doing now ?____ C、They're Daming's grandparents .
⑷Was your father a teacher ?____ D、No , I didn't .
⑸Who are they ?____ E、She's reading a book .
下列说法不正确的是( )
我国有多种动植物的分布,其原因是( )
已知:碳酸钠比较稳定,加热时不分解;2NaHCO3 △_ Na2CO3+CO2↑+H2O
图中B处为两个单向阀:推注射器时A1关闭,A2处打开;拉注射器时,A1打开进空气,A2关闭.
(一)实验步骤 ①组装好装置,检查气密性 ②反复推拉注射器 ③称量E、F的质量 ④关闭弹簧夹,加热D处试管直到反应不再进行 ⑤打开弹簧夹,再次反复缓缓推拉注射器 ⑥再次称量E、F的质量.
(二)问题探究: