唐代灭亡后出现的分裂局面到______建立以后结束[ ]
A．五代
B．南宋
C．北宋
D．蒙古
答案：C
So difficult____it to acquire a large vocabulary without the help of a teacher that he was close to giving up .
A．he have felt
B．have he felt
C．he did feel
D．did he feel
则Q1和Q2的关系为（ ）
A．Q1＞Q2
B．Q1=Q2
C．2Q1＜Q2
D．Q1=1/2Q2
O2（g）=H2O（g）；△H=-Q1 kJ/mol；2H2（g）+O2（g）=2H2O（l）；△H=-Q2 kJ/mol