Think about all of the ways that a scientist could test the hygiene hypothesis. If you were doing a correlational study in humans, what independent variables would you need to consider? If you were doing a manipulative study in mice, what variables would you need to control? What dependent variable would you measure?

Age, gender, culture of candidates.

If the research was performed in mice, living conditions should be controlled.

Dependent variables: Hygiene level.

Explanation:

First of all, the study in human beings should consider about differences in ages, genders, and cultures. Because in different ages, people have different expectation of hygiene. It is similar for gender in which female is probably more hygiene than male. There is not any specific place or country in which this study would be held. However, in general, many cultures define differently the hygiene, such as Western Asia, Eastern Asia, European, and so on.

Second of all, if they are doing the experiments on mice, they should consider about living conditions. These are the main variables, which impact on hygiene levels.

Lastly, because it is the study about a hygiene hypothesis. Thus, the hygiene levels should be consider.  

answer: populations of walruses and polar bears will decline

explanation:

you put it

i believe it would be c: tons.