Biology

The correct answer is: B.the plants should be exactly the same (size, health, age).

Here’s why:

In a controlled experiment, it is important to ensure that any differences in the outcome (in this case, plant growth) are due to the variable you are testing—in this case, fertilizer. To do this, the plants must be as identical as possible at the start of the experiment. This includes ensuring that they are the same species, size, health, and age, so that differences in growth can be attributed to the fertilizer, not pre-existing differences between the plants.

Let’s break down the other options:

A.The plants can be different species: This would introduce variability that could affect the results. Different species of plants may have different growth rates and responses t...