@Lucasl, what exactly do you mean by your question?
The reason that (A) is correct is because it if were true, then it would be impossible for it to be easy to grow cacti or orange trees in most of the country in question. Most means more than half, and if half of the country is difficult to grow cacti or orange trees in, then at most half of the country would be easy to grow cacti and orange trees in. Half is not most, as most has to be more than half, so this is why (A) must be false and is the correct answer choice.
Does this answer your question? Let us know if you'd like further clarification!
