若a>0，b>0，且函数f(x)＝4x³－ax²－2bx－2在x＝1处有极值，则ab的最大值为(　　)

A．2

B．3

C．6

D．9

The old couple have been married for 40 years and never once ________ with each other.

A．they had quarrelled

B．they have quarrelled

C．have they quarrelled

D．had they quarreled