What do Bill and Lucy decide to do?

Analysis:

The dialogue shows Bill and Lucy discussing their plans. Bill initially suggests that it's difficult to choose because there are many options. He then proposes trying scuba diving, while Lucy suggests trying jet skiing and possibly swimming with her parents in the afternoon. Lucy then states she'd rather not join them for swimming as she'll be tired after scuba diving.

Bill's final suggestion is: "Don't worry! I'll swim and you can just sunbathe!" Lucy agrees to this with "Oh... OK then!".

Conclusion: Bill decides to go scuba diving, and Lucy decides to go sunbathing. Bill will swim, and Lucy will sunbathe.