A:
B:
C:
D:
已知二次函数y=ax2+bx+c(a>0)的图象与x轴交于A(x1,0)、B(x2,0)(x1<x2)两点,与y轴交于点C,x1,x2是方程x2+4x﹣5=0的两根.
竞争是基于一定规则进行的,我们在竞争中必须遵守的基本准则是( )
In April, 2009, President Hu inspected the warships in Qingdao, ______ the 60th anniversary of the founding of the PLA Navy.
下列不属于基因遗传病的是( )