Macrophages are cells that play a role in the response of the immune system of
mice and other mammals to invasive organisms such as bacteria. Unlike other
mice, mice that are genetically incapable of making these particular cells do not
show elevated levels of nitrates when infected with bacteria. The statements
above, if true, provide the most support for which of the following
conclusions?

A. Mice that are unable either to make macrophages or to make them in sufficient
numbers will protect themselves from bacterial infections in some other way.
B. Mice that show elevated levels of nitrates can easily fight off most types of
bacterial infections.
C. In mice, macrophages play a role in the production of nitrates or inhibit a
process by which nitrates are broken down or otherwise eliminated.
D. When a healthy mouse becomes infected with an invasive organism, the number
of macrophages in the mouse's body decreases.
E. Injections of nitrates into mice that lack macrophages will not enhance the ability
of these animals' immune systems to fight off infection