We are conducting an experiment with a 2x2 factorial design to investigate the effects of soil type (fertilizer vs no fertilizer) and plant breed (heirloom vs non-heirloom) on plant height. In our analyses, we calculate the main effects of fertilizer and plant breed on height. We also calculate the interaction of fertilizer and plant breed on height.

Which of the following would be evaluated to determine "main effects?" [choose all that apply]

The mean difference between non-heirloom and heirloom plants in height, collapsing/averaging across soil type

How the mean difference in height between heirloom and non-heirloom plants depends on getting fertilizer vs. not

That the effect on height of getting fertilizer vs. not getting fertilizer depends on plant type (is different for heirloom vs. non heirloom plants)

The mean difference between plants getting fertilizer and those not getting fertilizer on height, collapsing/averaging across soil type