Find ways to praise your children often,_________ you’ll find they will open their hearts to you.

A．till

B．or

C．and

D．but

下列哪类细胞不表达MHC-Ⅱ类分子

A．B细胞

B．巨噬细胞

C．人活化的T细胞

D．树突状细胞

E．肝细胞