easy · Enhanced ACT science

A student investigated whether a liquid plant food increases the height of radish seedlings. She filled four identical pots with the same soil and planted five radish seeds in each. Pots 1-3 were watered daily with 20 mL of water mixed with 5 mL of plant food. Pot 4 was watered daily with 20 mL of plain water only. All four pots were kept under the same lamp at the same temperature. Which pot serves as the control in this investigation?

1. Pot 1, because it was simply the first of the four pots to be prepared and planted.
2. Pots 1-3, because they each received the liquid plant food that is being tested.
3. Pot 4, because it received the same treatment as the others except for the plant food.
4. All four pots, because every one of them was kept under identical light and temperature.

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