Here os the OE:

(Appropriate Preposition) Two of the choices have the expression “grounds to,”
while one has “grounds for.” Two other choices introduce full subordinate clauses.
This indicates that there is perhaps an error relating to the use of a wrong preposition.
The correct preposition to combine with “grounds” is “for” and not “to.” (What were
the grounds cited by the magistrate for the acquittal of the accused? What are the
grounds for your suspicion that George is dishonest?) So, (A) is wrong.
(B) also has the same error, and can be discarded for that reason.
(C) has the idiomatic phrase “grounds for sympathizing with,” and is the answer.
Always consider a phrase more idiomatic than a clause—so you can easily reject
both (D) and (E) as being less elegant than (C).

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"grounds for" is the correct idiom ..So Option C is the answer