Question

a group of students wants to know what amount of a particular fertilizer will produce larger watermelons. which of the following is the best choice to answer their question?
students should conduct both an investigation of various fertilizers and a controlled experiment where they change the amount of the particular fertilizer for watermelon plants and measure the differences.
students should make observations of various fertilizers.
students should conduct a controlled experiment where they change the amount of fertilizer for watermelon plants and measure the difference in size of the watermelons.
students should conduct a controlled experiment where they change the amount of fertilizer for watermelon plants and measure the difference in size of the watermelons.

Explanation:

The goal is to find the amount of a specific fertilizer for larger watermelons. A controlled - experiment changing only the amount of that particular fertilizer and measuring watermelon size differences is the most direct approach. Investigating various fertilizers is not necessary as the focus is on one specific fertilizer. Just making observations of various fertilizers won't answer the question about the amount of the specific fertilizer for larger watermelons.

Answer:

Students should conduct a controlled experiment where they change the amount of fertilizer for watermelon plants and measure the difference in size of the watermelons.