— Mr. Smith never means what he says. I dislike him.

—       , as the saying goes.

A．A single flower does not make a spring

B．A still tongue makes a wise head

C．A man of words and not of deeds is like a garden full of weeds

D．Actions speak louder than words

木块A、B分别得50 N和30 N，它们与水平地面之间的动摩擦因数均为0.2.与A、B相连接的轻弹簧被压缩了5 cm，系统置于水平地面上静止不动．已知弹簧的劲度系数为100 N/m.用F＝1 N的不变力作用在木块A上，如图所示．力F作用后(　　)

A．木块A所受摩擦力大小是4 N，方向向右

B．木块A所受摩擦力大小是9 N，方向向右

C．木块B所受摩擦力大小是9 N，方向向左

D．木块B所受摩擦力大小是6 N，方向向左