Final answer:
A good topic sentence introduces the main idea of the paragraph. 'My parents' grandfather clock has three main parts' is an example of an effective topic sentence because it provides a clear direction for paragraph development.
Step-by-step explanation:
A good topic sentence for an example paragraph should introduce the main idea that will be developed throughout the paragraph. Option OA, 'My parents' grandfather clock has three main parts', effectively sets up a paragraph that could outline and describe those three parts in detail. This sentence provides a clear and concise topic that the writer can expand upon with reasons, illustrations, explanations, or evidence. The other options are less effective as topic sentences either because they don't provide a clear direction for development (OB and OC) or because they make a subjective claim that would need to be supported by argument rather than examples (OD).