Hi, this is essentially a must be true question, the right answer is something the author must believe. Since the author claims that this method will eventually deplete all forests, she must not think that the forests will grow back faster than they are destroyed. If they did grow back faster, then the forests would not be completely eradicated. So, she must agree with A.
She does not have to agree with B, so what if there are no better means of tropical agriculture? One could import food instead.