Yusef wants to do a study on how students behave in school when there is a teacher and another adult in the classroom. how can yusef observe the behavior?
a. by asking the students if they prefer to have one or two adults in the classroom at a time
b. by first watching how students react when there is one adult in the classroom and then observing how they react when there are two
c. by interviewing teachers to find out if they prefer to have one or two adults in the classroom at a time
d. all of the above