Use the Following Information to Answer Questions (1) - (3)

Use the following information to answer questions (1) - (3) . Scientists were interested in determining if
the amount of nicotine present in tobacco leaves is related to the amount of water received by the plants.
In a greenhouse, a total of 120 tobacco plants were selected. During the growing season, 30 plants were
randomly assigned to receive the normal amount of water, 30 plants received 75% of the normal amount
of water, 30 plants received 50% of the normal amount of water, and 30 plants received 25% of the
normal amount of water. At the end of the growing season, one leaf was selected at random from each
plant and the amount of nicotine present was recorded for each. Researchers determined that leaves from
tobacco plants receiving the normal amount of water during the growing season had more nicotine than
leaves from tobacco plants receiving less water.
-Was this an observational study or a controlled experiment?

A) Observational study because the plants were not a random sample.
B) Observational study because the researchers determined how much water each group of plants would receive.
C) Experimental because researchers determined, through randomized assignment, which plants belonged to which treatment group.
D) Experimental because the researchers could not control the amount of nicotine in the plants.