The correct answer is D. mob - move.
The root is the basic part of a word which is used to create other words by adding prefixes and suffixes to it. Here, that tiniest part of the word immobilize is mob, which comes from Latin and means to move. By adding the prefix im- you created the negative form of the verb, and by adding the suffix -ilize, you created that particular verb.
This question is incomplete because the text is missing, here is the text:
Read the caption from When Birds Get Flu by John Consiglio.
Epidemiologists worried that one or two sick chickens could infect a whole town. And that town could infect the country—or even the world.
The answer to this question is A. Reinforce the case study's point that bird flu is dangerous.
Explanation:
"When Birds Get Flu" focuses on avian influenza and its implications not only for animals but for humans. In this text, its author John DiConsiglio explores the implications of disease and especially how dangerous it can be.
Moreover, this idea of bird flu as a major threat is supported by details such as "Epidemiologists worried that one or two sick chickens could infect a whole town..." because this shows the disease spread easily from one area to another as one single chicken could infect other chickens or infect people and this was likely to lead to a pandemic. According to this, the main purpose of this caption is to reinforce or show the danger of bird flu.