how would you use the scientific method to answer this question: do mice live longer when they are fed high-sugar diets

The question: Do mice live longer when they are fed high sugar diets?

Hypothesis: There are two hypothesis the null hypothesis which we assume is correct, it states that a high sugar diet will have no effect on the life span of a mouse and an alternate hypothesis that we accept if evidence shows that sugar does increase the life span if mice. It says a high sugar diet does incerease the life span of mice.

Prediction: Assume that the null hypothesis is correct. High sugar diets will not increase the life span of the mice.

Collect data through experimentation. Use some mice as a 'control'. These mice will not undergo any changes but will be kept for comparison. Expose some other mice to high sugar diets and the compare the outcome with the 'control' mice.  

Analyzing: From the experiment this you can choose which hypothesis you are going to accept. I.e. null: no change or alternate: there was a change and do some extra research to back up your hypothesis.

Hope this helps :)

the answer is:

carbon dioxide