I would respond by acknowledging that indeed an apple does have cells, but that does not necessarily make it a living thing. While it is true that living things have cells, there are other criteria that must be met in order for something to be considered living.
Living things are characterized by their ability to grow, reproduce, respond to stimuli, and maintain homeostasis. An apple, on the other hand, does not have the ability to do any of these things. It cannot grow or reproduce, nor can it respond to stimuli or maintain homeostasis.
Additionally, while an apple does contain living cells, those cells are not actively carrying out the functions necessary for life. They are essentially in a state of suspended animation until the apple begins to decompose.
Overall, while it is understandable that someone might assume an apple is a living thing due to the presence of cells, a more comprehensive understanding of what constitutes life would lead one to conclude otherwise.