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Q32:

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?

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. Mice that show elevated levels of nitrates can easily fight off most types of bacterial infections. In mice, macrophages play a role in the production of nitrates or inhibit a process by which nitrates are broken down or otherwise eliminated. When a healthy mouse becomes infected with an invasive organism, the number of macrophages in the mouse’s body decreases. Injections of nitrates into mice that lack macrophages will not enhance the ability of these animals’ immune systems to fight off infection.

Answer:

I chosed C.

The premise of the sentence have two part: 1.Macrophages play a role in the response invasive organisms such as bacteria. 2.mice without Macrophages do not show elevated levels of nitrates when infected with bacteria Here we see a gap between "elevated levels of nitrates" and "Macrophages play a role in the response".

C tell us the relationship between "Macrophages's role" and "nitrates", and that build a bridge on the gap, and make this sentence perfect.

However, A is out of scope talking about mice unable either to make macrophages or to make them in sufficient numbers

to be discussed...