反应A+BC分两步进行:①A+BX,②XC,反应过程中能量变化如图所示,E1表示反应A+BX的活化能。下列有关叙述正确的是( ) E2表示反应XC的活化能 X是反应A+BC的催
下列属于生物因素对生物影响的是 （ ）A.春来江水绿如蓝 B.种豆南山下，草盛豆苗稀C.雨露滋润禾苗壮
______ about wild plants that they decided to make a trip to Madagascar for further research． A．So curious the couple were B．Such curious the couple were
--This desk is too heavy．I _______ move it．Could you help me? --No problem． A．can B．can't C．should D．should
下列化学反应的离子方程式正确的是（ ） A．在稀氨水中通入过量CO2:NH3·H2O+CO2=NH+HCO B．少量SO2通入Ca(ClO)2溶液中：SO2+H2O+Ca2++2ClO-=CaSO3+2HC
甲地海拔400米，乙地海拔200米，则甲乙两地相对高度： A．400米 B．200米 C．600米
I’ve started driving again. I drove along a road ___21___ 12 years ago near my home. As I drove tonight I___22___Kelly. Kelly was a ___23___ when it was constructed. She and her brother were ___2
已知二次函数的两个实数根分别是 （1）设函数的对称轴为 （2）如果
,则
是 ( )
(B) 
(D) 
,∴