Final answer:
The best topic sentence for a paragraph on the impact of the legend of Loch Ness is option B, as it provides a broad yet clear indication of the paragraph's subject—the economic impact of the monster's legend on tourism. Therefore, the correct option is B.
Step-by-step explanation:
The best topic sentence for your paragraph would be B. The legend of the Loch Ness monster has made Loch Ness a lucrative tourist attraction. A topic sentence effectively summarizes the main idea of your paragraph and captures the reader's attention. Here, option B provides a clear topic that can be developed throughout the paragraph by discussing both the economic impact of the legend (the cause) and the various ways in which the lore of the monster generates revenue (the effects), such as merchandise sales, tours, and accommodation for visitors searching for the mysterious creature.
In contrast, while option A mentions people traveling to Loch Ness, it does not cover the broader implications that make for a well-developed topic sentence. Option C limits the scope to boat cruises, which might not present a comprehensive picture of the overall tourist attraction that Loch Ness represents. Thus, for a paragraph that aims to explore the legend's economic impact on the area, option B is the most suitable.