Choice D is the best answer because it most accurately states the main idea of the text. The text describes Mary’s activities in an overgrown hidden garden, saying that she was “very much absorbed” and was “only becoming more pleased with her work every hour” rather than getting tired of it. She also thinks of garden activities as a “fascinating sort of play.” Thus, the main idea of the text is that Mary feels very satisfied when taking care of the garden.
Choice A is incorrect because the text never makes any mention of Mary’s chores. Choice B is incorrect because the text indicates that Mary finds pulling up weeds to be fascinating, not boring. Choice C is incorrect because Mary thinks of garden activities in and of themselves as play, not as something necessary to do to create a space to play.