A firm has a production function f（x，y）=1：10（x0.20 + y0.20）5 whenever x > 0 and y > 0.

A.increasing returns to scale.

B.decreasing returns to scale.

C.constant returns to scale.

D.increasing returns to scale if x + y > 1 and decreasing returns to scale otherwise.

正确答案：increasing returns to scale.