Explanation

The first half of this sentence tells you that you’re going to focus primarily on the painter’s personality. You then need something that contrasts with either “pretentious” or “pontificating.”

Artless and ingenuous, meaning “without effort or pretentiousness,” are perfect. Shrewd, adroit, and artful are all positive words, but they don’t contrast with “pretentious” or “pontificating.”

Hence options artless, ingenuous are correct.