Answer:
A diamond shape
Step-by-step explanation:
A topic sentence of a paragraph, which it's its controlling idea, may be placed at the beginning of a paragraph (The most common placement), in the beginning and in the end of it, in the end only, or, less common, it can be in the middle of a paragraph.
When the topic sentence is in the medial position, the sentence provides a transition between two ideas that are closely related to each other (For example, the causes and the consequences of something), and the paragraph should have a diamond shape, in which the wider portion of the shape contains the topic sentence, so that the topic sentence has more focus.