Nathan entered the cellar. Mason entered the cellar. The watermelon is in the green bathtub. Mason exited the cellar. Nathan moved the watermelon to the green suitcase. Mason entered the cellar.
The watermelon at the beginning was in the green bathtub.
 the watermelon at the beginning was in the green_suitcase
 the watermelon at the beginning was in the green_bathtub