What is a key characteristic of the topic sentence in a letter?

The key characteristic of the topic sentence in a letter is that it introduces the main idea of the paragraph. A well-crafted topic sentence sets the tone and focuses the reader on what the paragraph will discuss. This is critical in a letter, particularly in a professional context like the Occupational English Test, where clarity and directness are essential.

When the topic sentence clearly outlines the main idea, it helps the reader understand the purpose of the paragraph right away. This is especially important in letters related to healthcare, where the information can be technical or complex. By clearly stating the main idea, the topic sentence ensures that the rest of the paragraph will provide supporting details and explanations that are relevant and help in conveying the intended message effectively.

Other elements like summarizing the entire letter or containing the salutation are less appropriate here, as the topic sentence is meant to focus on a specific point rather than encompass everything or serve as an introduction. Providing detailed patient history may also be important in certain contexts but does not define the essence of a topic sentence, which should succinctly introduce the main content of the paragraph it leads.