Question

A researcher is interested in finding out if the amount of amylase, a digestive enzyme found in saliva responsible for digesting starch, varies from person to person. Which of the following would be the best way to test this?
Take consistent amounts of saliva samples from a number of people whose meal times vary and measure the quantity of amylase in each sample.

Take consistent amounts of saliva samples from a number of people who have not eaten in 8 hours and measure the quantity of amylase in each sample.

Take varying amounts of saliva samples from a number of people whose meal times vary and measure the quantity of amylase in each sample.

Take varying amounts of saliva samples from a number of people who have not eaten in 8 hours and measure the quantity of amylase in each sample.

Answer 1

Take consistent amounts of saliva samples from a number of people who have not eaten in 8 hours and measure the quantity of amylase in each sample.Taking consistent amounts of saliva allows the experiment to be controlled, and also all after 8 hours is also being consistent. Just varying who produces the saliva is the scientific method, trying to limit the variables to one thing at a time so the results are easier to interpret.

Answer 2

The answer is Take consistent amounts of saliva samples from a number of people who have not eaten in 8 hours and measure the quantity of amylase in each sample.

First, the researcher needs to know the quantity of amylase in the same amount of saliva. Thus the amount must be consistent and not varying. 
Next, people must not eat in 8 hours, so they are all in the same condition at the moment of collecting saliva. If some eat immediately before the sample collecting while some eat 8 hours before, the content of their saliva will be different. 
For the correct results, all conditions must be the same.