Several Researchers Are Working on Different Experiments That Are Designed

Multiple Choice

Several researchers are working on different experiments that are designed to test whether a person's confidence can be changed over time.They want to be able to compare their results when they are done.They agree that they will all use the same test in order to measure confidence.What have the researchers done

A)  They agreed to use the same independent variable. 
B)  They agreed to use the same hypothesis. 
C)  They agreed on an operational definition of confidence. 
D)  They agreed to remove a confounding variable.