--- Excuse me. Is there a pay phone near here?
--- No, . Maybe you can ask the police.
A:there isn't
B:it isn't
C:they aren't
D:that isn't
As long as I can remember,________I called,my son would answer.( )
取锌、铜的混合物8g与154.7g稀硫酸恰好完全反应,称得剩余物质的总质量为162.5g.请计算:
(1)产生氢气的质量是多少?
(2)反应后所得溶液中溶质的质量分数是多少?
下列对划线字的解释说明不正确的一项是( )
人工选择指在生产和生活实践中,人们根据自己的____和____,不断____和____生物新品种的过程。