A:CH4(g) + 2O2(g) ='=' CO2(g) +2H2O(l) ΔH=-890 kJ·mol-1
B:2CH4(g) + 4O2(g) ='=' 2CO2(g) + 4H2O(l) ΔH= +890 kJ·mol-1
C:CH4(g) + 2O2(g) ='=' CO2(g) +2H2O(l) ΔH= +890 kJ·mol-1
D:2CH4(g) + 4O2(g) ='=' 2CO2(g) + 4H2O(l) ΔH= -890 kJ·mol-1
若一次函数y=(3-k)x-k的图象经过第二、三、四象限,则k的取值范围是( )
美国“肯尼迪号”航空母舰上有帮助飞机起飞的弹射系统,已知“F-A15”型战斗机在跑道上加速时产生的加速度为4. 5 m/s2,起飞速度为50 m/s,若该飞机滑行100m时起飞,则弹射系统必须使飞机具有的初速度为( )
唐朝衰亡与东汉衰亡的相似之处有( )
①统治者贪图享乐②任用奸臣③发生了人民起义④外戚宦官专权
A. It is on the desk.
B. I help my mum and dad.
C. He does his homework.
D. She draws a picture.
E. It's a TV.