The correct answer is D. Sentence 1
Step-by-step explanation:
In writing, the topic sentence is the sentence in a paragraph or text that summarizes what the paragraph or text is about or the main idea of it. This implies, the topic sentence tells the reader the content he will find while reading a paragraph or text, because of this, it is common the topic sentence is the first sentence or are placed at the beginning of paragraphs and connected to all the details provided by the author in subsequent sentences.
In the case of the excerpt presented from "We’ll Never Conquer Space" by Arthur C. Clarke, which is composed of four main sentences, the sentence that works as a topic sentence is sentence 1 "To our ancestors, the vastness of the Earth was a dominant fact controlling their thoughts and lives" because this sentence summarizes the main idea of the paragraph which is the concept of "vastness of Earth" our ancestors had, which is developed through the subsequent details presented in sentence 3, 4 and 5 that are mainly examples of the main idea and help to explain it.