.In a particular production process, if the quantities of all inputs used are increased by 60 percent, then the quantity of output increases by 70 percent as well.This means that

a.

the production process cannot be enhanced by technological advances.

b.

no mathematical representation of the relevant production function can be formulated.

c.

the relevant production function has the decreasing-returns-to-scale property.

d.

the relevant production function has the increasing-returns-to-scale property.