The option which does not contribute to the overall dreary mood of the excerpt are infinitive phrases.
The reason why that is the correct answer is because there are no infinitives or infinitive phrases in the excerpt above, which immediately means they cannot contribute to any mood whatsoever. The other options are present in the passage above and thus have an effect on the story, the setting, and the overall mood of the excerpt itself. Repetition is especially effective when it comes to creating dreary mood here, because it is constantly telling us that fog is everywhere.