Scientists Are Always Thinking About Ways to Improve Experimental Design

Scientists are always thinking about ways to improve experimental design.In the text's potato chip experiment,which of these changes would produce the most effective design?  

A) Show a different movie.
B) Exclude teenagers as group members.
C) Collect uneaten chip remains and weigh them for both groups.
D) Provide free drinks before the experiment.
E) Use a smaller theater.