Which of the following statements about Langerhans’ cells is TRUE

A．They commonly are found in the dermis

B．They function as sensory mechanoreceptors

C．They function as receptors for cold

D．They play an immunologic role in the skin

E． They are of epithelial origin

决定国际间资本流动的主要因素是各国的（）。

A． 收入水平

B． 利率水平

C．生产力水平

D．价值水平