Explanation

In the part following “since,” the first sentence of the paragraph suggests that the subject matter of portraits might not seem to fit with the idea of “high art.” So the suggestion is that the presence of portrait paintings in art museums is in that sense odd or unfitting. Of the choices available for Blank (i), “surprising” is the one that expresses this sense. The second sentence, in contrast to the first, offers a point in favor of portraits
— “artistic skill.” So the second sentence is offering a reason why portraits should be in art museums. Of the choices for Blank (ii), “justifies” is the one that completes that thought.
Thus the correct answer is surprising (Choice A) and justifies (Choice E).