A "poker face" (Line 3, Para. 2) refers to a face which is ______ .

A．maintain direct eye contact
B．hide emotions with a deadpan expression
C．display excitement or disgust, shock or sadness
D．raise their eyebrows, nod and smile politely

A．should be avoided
B．is universal among parents
C．sets up dangerous states of worry in the child
D．will make him lose interest in learning new things