Answer:
The appropriate description of this sentence is Both a and b
Step-by-step explanation:
A thesis statement is a sentence that expresses the main idea of any kind of written work, it could be from research, an essay, etc., while a topic sentence organizes the paragraph by summarizing the general information in the rest of the reading. the sentence covers the two functions since it is focused on the main topic as it generally talks about the events in the story.