The argument is that a transition from fossil fuels to biofuels is necessary. We must look for statements that weaken this argument, i.e. statements which say that transition from fossil fuels is not necessary.
1 – Wrong
If longer growing seasons and other impacts of climate change will lead to increased food harvests, it is will be feasible for the transition from fossil fuels to biofuels to occur. So this does not weaken the argument (instead it strengthens it).
2 – Wrong
Again, this statement shows how biofuels can be easily produced and hence, does not weaken the argument.
So D is the answer.