IMO - B
From My notes:
"Less" refers to a smaller number or quantity, usually of something uncountable (and thus singular).
There is less water in the bucket than in the pool.
I have been trying to cut back, so now I drink less coffee.

However, we can use "less" to refer to something plural if it is a measure of time, money, or distance.
The red sweater is on sale for $10 less than regular price.
The distance to the grocery store is 3 miles less than the distance to the restaurant.
Felicia spoke to the group for less than 5 minutes.

(The idea behind this exception is that time, money, and distance are all uncountable as bulk quantities, so we use "less" as the comparison word even though we have countable units of measure for these quantities.)

Typically we would use "few/fewer" to refer to a smaller number of countable (and thus plural) items.
Express checkout: 10 items or fewer.
Gene has read only a few books on the assigned reading list.

"Lower" is the comparative of "low," so it should only be applied to things that could be described as low.
The average temperature is lower in the winter than in the summer.
Lower the water level in the pool by pulling the drain plug.

IMO B

We can eliminate C D E
c) Using past perfect is not required. Simple past is good.
d) than one would have..but in the sentence it is written your...so eliminated
e) Using Present Perfect is not required.

Now it is btw A & B... and as Target has mentioned, Lower is much better to use here.

Thanks
Gautam

Great post Abhishek. Thanks.