Pointing out the benefits of the GST within a month of its implementation, Modi said that goods are being transported much faster, highways have become clutter-free and pollution levels had gone down and increased speed of trucks.

(I) are being lowered with the decreased

(II) have come down with the increased

(III) have been lowered because of decreasing

“have come down with the increased” is the correct phrase to make the sentence grammatically correct as the sentence is in Present Tense. It is to be noticed that the speed of trucks can’t be decreased as it is clearly mentioned that the highways have become clutter-free. Thus the options (I) and (III) can be easily eliminated. Also, the phrasal verb “come down” means collapse or be demolished. Hence 2 is the correct option.