(need asap) an investigation was set up to determine the effectiveness of a particular fertilizer on the growth of bean plants. in the investigation, each of the 10 bean plants in group a was watered with 50 milliliters of a solution of distilled water and fertilizer, while each of the 10 bean plants in group b was watered with 50 milliliters of distilled water only. both groups of plants were watered every other day for 1 month and grown under identical environmental conditions. the control group for this investigation was. .

a. group a only

b. group b only

c. both group a and group b

d. neither group a nor group b