[JEM]

MOTU,

(A) is the correct answer for two reasons:

First, in (B) "their" is ambiguous.

Second, in (B) the parallelism between "their" and "that" is not grammatical. I.e. the form: "not so much their X as that Y" is incorrect. The proper form is: "not so much that X as that Y.

Hope that helped.

JEM