The operation " $\nabla$ " is defined by $(a, b) \nabla(c, d)=a c+b d$.

For example $(1,2) \nabla(3,4)=(1)(3)+(2)(4)=11$.

The value of $(3,1) \nabla(4,2)$ is
(A) 10
(B) 11
(C) 13
(D) 14
(E) 24
From the definition, $(3,1) \nabla(4,2)=(3)(4)+(1)(2)=12+2=14$.

ANSwER: (D)