Mrs Read __________ the cleaning every day.
A:doesn’t
B:doesn’t do
C:don’t do
D:didn’t do
设数列an是等差数列,且a2+a3+a4=15,则这个数列的前5项和S5=( )
已知二次函数y=ax2+bx+c(a≠0)的图象如图所示,有下列结论:①b2﹣4ac>0;②abc>0;③8a+c>0;④9a+3b+c<0其中,正确结论的个数是( )
There ____ a book and two pens on the desk.