A – Correct
This is the only sensible option out of the 4 given. If sales of a new antibiotic are controlled, then there are less chances of developing drug-resistant bacteria.
B – Wrong
This would, in contrast, weaken the argument. Since some countries allow antibiotics to be bought without prescription, people can argue that the local government can also do the same.
C – Wrong
No viruses mentioned in the text.
D – Wrong
The text says nothing about livestock, so we can eliminate this straight away.