To best support Alexis's argument about reforesting old pastures to help the Amazon rainforest recover, the most relevant statement is:
D. Old pastures can be reforested with little effort by planting native seeds on them.
This statement directly supports her proposal by emphasizing that reforesting is a feasible action that can be done easily, aligning with her argument for taking action to mitigate the effects of deforestation.
The other options, while true, do not directly support her specific argument about reforesting old pastures.