Sentence Correction

By showing that South Africa does not have a free market and is in fact a kind of collectivist welfare state for Whites only, Sowell argues that American conservatives have no valid ideological grounds to be in sympathy with the Pretoria regime.
(A) to be in sympathy with
(B) to sympathize with
(C) for sympathizing with
(D) that they should sympathize with
(E) that they should have sympathy for

OA C
Why not b

because correct idiom is "grounds for " and not "grounds to"

rohan_vus wrote:because correct idiom is "grounds for " and not "grounds to"

can someone confirm if "on grounds of " a correct idiom ? I tried looking up in dictionary but didn't help much. But I remember a statement vaguely " he was convicted on grounds of ...."
is this usage right?

Another reason is the fact that the people are sympathizing over a period of time, which 'sympathizing' emphasizes.