Pick and copy all the incorrect options for the following question:

A student investigated the effect of iron on the growth of plants. Four identical plants received a different amount of iron supplement when being watered. This investigation could have been improved if there were

Options:
- earthworms in the soil.
- fewer plants in the experiment.
- plants that received water without iron supplements.
- plants that received different amounts of sunlight.



- earthworms in the soil.



- fewer plants in the experiment.





- plants that received different amounts of sunlight.

