You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Scientists have discovered that there has been a reduction in the butterfly population in an ecosystem. After much research, they have identified that the carrying capacity for butterflies has been decreased. If the scientists want to increase the butterfly population, which action should they recommend?
(A) removing primary producers (B) spraying of insecticides (C) increasing runoff (D) planting flowers
D