Answer:
A. Repetition; prevents
Explanation:
For writers and speakers, it's very important to keep their audience focused on them and their work. If every sentence sounds the same, the text will become repetitive and the readers/listeners will get bored very soon. That's why it's important to vary sentence patterns, for example, to vary the subject of the sentences, break up long sentences (especially complex ones), use a dependent clause before the subject instead of the opposite, etc.
