The correct option is C watching a horror film
The phrases that are compared in a sentence should be parallel to each other in their grammatical structure. The latter phrase ("a horror film") should be of the same structure as the former ("attending the meeting"). Since the latter does not follow the former in structure, it needs to be changed and, hence, option D is incorrect. Option A is incorrect because the demonstrative 'that' is used to modify nouns and not gerunds, but the option modifies the gerund 'viewing'. Option B is incorrect because it does not follow the same structure as the former phrase, where the option has the combination 'noun + adjective + noun' while the structure required is 'gerund + noun'. The phrase in Option C is consistent with the structure of the former phrase "attending the meeting", hence it's the correct answer.