Critical Reasoning

A cup of raw milk, after being heated in a microwave
oven to 50 degrees Celsius, contains half its initial
concentration of a particular enzyme, lysozyme. If,
however, the milk reaches that temperature through
exposure to a conventional heat source of 50 degrees
Celsius, it will contain nearly all of its initial
concentration of the enzyme. Therefore, what destroys
the enzyme is not heat but microwaves, which generate
heat.
Which one of the following, if true, most seriously
weakens the argument?
(A) Heating raw milk in a microwave oven to a
temperature of 100 degrees Celsius destroys
nearly all of the lysozyme initially present in
that milk.
(B) Enzymes in raw milk that are destroyed through
excessive heating can be replaced by adding
enzymes that have been extracted from other
sources.
(C) A liquid exposed to a conventional heat source
of exactly 50 degrees Celsius will reach that
temperature more slowly than it would if it
were exposed to a conventional heat source
hotter than 50 degrees Celsius.
(D) Milk that has been heated in a microwave oven
does not taste noticeably different from milk
that has been briefly heated by exposure to a
conventional heat source.
(E) Heating any liquid by microwave creates small
zones within it that are much hotter than the
overall temperature that the liquid will
ultimately reach.