Thank you for this!

Congratulations! This is awesome

This is sort of late, but the way I thought about it is that pigweed seeds MUST be exposed to sunlight if they are to germinate. Even if you make sure they're redeposited into the soil, without sunlight, burying them again doesn't guarantee that they will germinate. Sunlight must be part of the equation for that to occur, and answer choice D leaves that out.