The OA is actually (A).
The question says:
decreased by 20%
For example: Quantity of sugar decreased by 10% (of the original quantity). It means that if it were 100%, now it is 90% (of the original quantity).
In 1900 the salt concentration in Southern Lake was 4%
4% is of what quantity? Original?
Can someone please explain the question and specifically (2)?
Thanks a lot.