Dna is responsible for your phenotype, but to what extent?

Robert wants to know which fertilizer will work the best for his grass. what can he do to explore this inquiry?

Ineed to know why d is the correct answer asap

An ecologist studied the same species of deer during the summer and the winter. she noticed that during the summer, when there was plenty of food, the deer were energetic and playful. however, during winter when food was scarce, the deer moved more slowly and did not run unless they needed to escape a predator. which scientific fact is best supported by her observations?