脉络丛前动脉发自()

A．颈内动脉

B．大脑前动脉

C．大脑后动脉

D．大脑中动脉

E．基底动脉

The long-run production decision differs from the short-run production decision in that:（）

A. variable costs can be changed in the short run but not the long run.

B. variable costs can be changed in the long run but not the short run.

C. fixed costs can be changed" in the long run but not the short run.