I am afraid that this topic is suspect in terms of logic.
1. The first part says that mechanized farming costs more than traditional farming. In the next breath, it says costs have reduced to half by mechanization.
This year, If mechanization cost me 150 fifty rupees, some 50 rupees more than the 100 rupees that I spend for traditional method, the cost goes up but not cut by half.
Let us not confuse the cost of cultivation with yield. Corn yield doubled means, the grain yield went up from, say, some 100 kegs to 200 kgs. However, It does not automatically mean that the costs were cut to half.
Nor can we say that the eventual effective cost this year is half of the original cost, due to the doubled yield. This will happen only when the absolute cost remains the same as that of the traditional method. But, mechanization has increased the absolute cost, the topic says in the first part.
This topic does not seem to convey ant sensible meaning because all the choices say that the costs were cut to half.