函数f(x)的定义域为开区间(a,b),导函数f′(x)在(a,b)内的图象如图所示,则函数f(x)在开区间(a,b)内有极小值点( )
A:1个
B:2个
C:3个
D:4个
The summer holidays are coming, so the twins as well as Jack ________ to Hong Kong for vacation.