Official Explanation
It is possible to analyze this sentence by starting with either blank. Broadly, it states that something that has happened to Nabokov has called attention to some of his peripheral activities. It would hardly make sense for what had happened to be either stigmatization or marginalization, since both of those activities represent a turning away from him, not a calling attention to him. So the correct answer for the first blank is “lionization,” since to lionize means to treat as important. Then, since we are told that Nabokov is a literary giant, entomology must be one of his peripheral activities, so the correct answer for the second blank must be “foreground,” which also means “call attention to.” Spotlighting something would not result in transcending it or obscuring it, so neither of the other choices is correct.
Thus, the correct answer is lionization (Choice B) and foreground (Choice D).