What skill is primarily improved by reading a variety of texts at different difficulty levels?

Reading a variety of texts at different difficulty levels significantly enhances multiple literacy skills, which is why the most comprehensive choice is the most fitting.

Firstly, engaging with diverse texts exposes readers to a broader vocabulary. Different genres and styles introduce unique words and phrases, enriching a reader's lexicon and understanding of language in context.

Furthermore, this practice supports sight word recognition. Various texts can highlight common sight words in different contexts, promoting quicker recognition and understanding without needing to sound out each word.

Lastly, fluency is greatly enhanced through exposure to varied reading materials. As readers encounter different structures, rhythms, and patterns in texts, they become more adept at reading smoothly and with expression, which is key to overall reading proficiency.

Therefore, reading a wide array of texts positively impacts vocabulary exposure, sight word recognition, and fluency, making the most comprehensive option the best answer.