The Production Function Feature Called "Constant Returns to Scale" Means

The production function feature called "constant returns to scale" means that if we:

A) .multiply capital by z
And labor by z , we multiply output by z .
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B) increase capital and labor by 10 percent each, we increase output by 10 percent.
C) increase capital and labor by 5 percent each, we increase output by 10 percent.
D) increase capital by 10 percent and increase labor by 5 percent, we increase output by 7.5 percent.