The sentence contrasts the actor’s strong efforts with the movie’s poor performance
The first blank describes the actor’s efforts, which were strong and passionate, so (B) fervent best fits
The second blank describes the level of disappointment at the box officeWords like (E) major and (F) colossal indicate a significant scale, with (F) colossal emphasizing an especially large failure, matching the tone
The conjunction “despite” highlights the contrast between the actor’s efforts and the outcome