The correct answer is B. Have you noticed how hard she works?
Explanation:
In writing, sentence variety refers to using different types of sentences and grammatical structures to add variety to the text and make it dynamic and interesting. This implies using a complex and compound sentences rather than only simple sentences; using negative sentences and questions rather tan only affirmative sentences and using different tenses or beginning sentences with different sections.
In the case presented, the first and third sentence include are written in simple present and are affirmative sentences. Also, in the case of the first one it begins by using "Anna is" and therefore using other sentences in the present simple or that begin with "Anna is" is not recommended. Instead, the best is to use "Have you noticed how hard she works? " because this is in a different tense (present perfect), it is a question and also it does not begin using "Anna" which means it is different to other sentences and add variety.
