请教

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.
Answer:C, 我也觉得选Ｃ，但我是在排除Ａ，Ｂ，Ｄ，Ｅ之后得出的，对Ｃ我还是不太明白，请高手指点下，谢谢！

这是一个归纳题也可以看成是个解释题目，逻辑的推理过程是　有Ｍ－－－＞没有Ｂ，没有Ｍ，有Ｂ－－＞没有提高的Ｎ（原文有本应提高的意思．）

Ｃ说，在老鼠的身体中Ｍ有两个作用，１　Ｍ能生产出Ｎ，（顺应了之前两个推理的结合．）

　　　　　　　　　　　　　　　　　２　Ｍ抑制Ｎ的减少．（也是两个推理的结合．）