Less is normally used for uncountable items, though it can be applied to money etc, e.g. less water, less money.

Lower is comparable term of low, normally applied to countable items, but only where low is applicable, e,g low temperature, low temparement.

Here IMO C.

REdundancy : Amount to sum out A, E
Tense : Past required ed, out B
less/lower : Lower not applicable D

IMO C

The quest is for countable and uncountable .

Here we are talking about amount :-

Lower amount of money
Less amount of money

So options with less are to be sorted out for contenders i.e. B and C .

B loses track on subject verb agreement .

IMO C.

prachich1987 wrote:Even though the direct costs of malpractice disputes amounts to a sum lower than one percent of the $541 billion the nation spent on health care last year, doctors say fear of lawsuits plays major role in health-care inflation.

(A) amounts to a sum lower
(B) amounts to less
(C) amounted to less
(D) amounted to lower
(E) amounted to a lower sum

OA : after some discussion

SV Error : Sub is "Costs" - A,B out
Higher and lower are more typically used with numerical comparisons. So D, E out
IMO _ C

The OA is C

It may help to remember that even though individual items may be countable, the word for the total will be uncountable -- while you can count kilograms, you can't count weight; while you can count dollars, you can't count cash.