Ed has two citrus trees at his home. he keeps one outside on a shaded patio, and the other indoors near a large window and a lamp. the indoor tree receives more light and experiences more stable temperatures than the outdoor tree.

he noticed that the indoor tree grew faster and produced bigger oranges than the outdoor tree. he installed a grow-lamp near the outdoor tree so that it would receive as much light as the indoor tree, but there was no change: the indoor tree continued to outgrow the outdoor tree.

based on this investigation, what would be the next logical question that ed should address?