Owing to the slack demand ______ their products for the time being, they do not think it advisable to buy the machine.

A．of
B．for
C．on
D．in

“或为辽东帽，清操厉冰雪。”“或为渡江楫，慷慨吞胡羯。”说的是哪两个人的典故？（）

A.管宁、祖逖

B.祖逖、张巡

C.张巡、段秀实

D.段秀实、管宁