This question is testing an idiomatic structure that's not very common on the GMAT (or in spoken English): To ____ is to _____. This is setting up an equivalence between two infinitives: "doing one thing is in effect the same as doing the other thing."

Examples that I can think of from literature / common expressions:

To love another person is to see the face of God. (Les Miserables)

To live is to die. (common expression, but also apparently a Metallica song)

To think is to perceive.

Etc.

So in this example, the subject of the sentence is the infinitive "to portray." The only structure that makes sense in this context is the idiomatic structure mentioned above: To portray virtue ... is to follow in a long tradition...

The only answer choice with that structure is C.

gmat4fun wrote:The sentence talks about a general fact and hence requires the usage of simple present tense. Only option C has the correct tense.

You're right that when we're talking about general facts, we generally want to use the present tense. That does not mean, however, that we're required to use the simple present tense, as opposed to the present progressive, etc.

Consider: When tourists hike to Machu Pichu, they are following trails that have existed for hundreds of years.

We can certainly use the present progressive to talk about what's generally true in this context.

In the sentence "To portray..." though, the issue was not simply that it was a general fact. We were using an infinitive as a subject, and the only way for that to make sense is in the idiomatic structure "to portray... is to follow..."