Which research method/design would you use to test the following hypothesis? The four choices are: surveys, observation, use of existing sources, and experiments. a. Eating a sugary lunch causes...

Which research method/design would you use to test the following hypothesis?
The four choices are: surveys, observation, use of existing sources, and experiments.
a. Eating a sugary lunch causes children to be sleepy during the class period following their lunch break.
b. Women do not pursue college degrees in mathematics to the same degree as men do because they are discouraged from doing so by their high school math teachers.
c. Pet owners are happier than non-pet owners.
d. In middle school boys and girls socialize primarily with members of their own sex.
If you were testing out the above hypothesis which research method(s) would be the most effective?
50 words.