17. Consider the absorption of gas A by a laminar falling film of liquid B. Gas A is only
slightly soluble in B, and the diffusion takes place so slowly in the liquid film that A
will not penetrate very far into B. The concentration of A at the interface is maintained
at CAo and the maximum velocity of the fluid is Vmar. Let x be the coordinate into the
liquid film, z the coordinate down the liquid film, and DAB the mass diffusivity of A in
B. The molar concentration of A, CA, is a function of x and z. Which of the following
statements is true?

(A) CA increases with increasing x.

(B) CA decreases with increasing z.

(C) CA increases with decreasing

at fixed x and z.

(D) CA decreases with increasing

at fixed x and z.