Traits were either dominant or recessive of either parents pea plant.
Essentially, a control variable is what is kept the same throughout the experiment, and it is not of primary concern in the experimental outcome. Any change in a control variable in an experiment would invalidate the correlation of dependent variables (DV) to the independent variable (IV), thus skewing the results.
with this option given I don't think there is an odd one
They both need nutrients and are able to reproduce
