The sugarcane production in the country is estimated at 2,712 million

I suspect this is not a question from the noted Manhattan Prep company and may be from the second ring company Manhattan Review, as once explained by generis in another topic.

Let me tell you why.

1. estimated at is wrong. We never make an estimate at a precise and fixed factor. Estimates are always to be since an element of variance is always inherent in them.
2. while the production is mentioned in million tons, the shortfall in 2007 production is mentioned in just tons. It should be also in million tons. The lack of proofreading has led to a gross error.

Now on to the question. I presume you were stuck between C and D, (precisely between less and fewer).

The compared factors should be between the production in, God only knows which year, on one hand, and the production in 2007. Since production is a mass factor, less is usable. Please do not go by the thought that since some countable things as tons are involved, the correct thing should be fewer. As you see, 2712 ton is not being compared here with 792 tons, as one is production and the other is a shortfall. Use of less is ok as I see.

You will not only save a lot of time by avoiding such questions but also not get stuck.