Which of the following production functions exhibit constant returns to scale?In each case y is output and K and L are inputs.

(1)y =K^1/2L^1/3

(2)y =3K^1/2L^1/2

(3)y =K^1/2+L^1/2

(4)y =2K +3L

a.2 and 4

b.2 and 3

c.1, 2 and 4

d.2, 3 and 4