which situation is an example of an observational study?

a. placing different groups of people in different colored rooms and recording their mood
b. finding the number of red jellybeans placed in an average jar of jellybeans by counting
c. dividing a class into thirds, giving each third a different amount of time to read, and then testing comprehension
d. having customers fill out a questionnaire about their favorite brand of toothpaste

 A.Placing different groups of people in different colored rooms and recording their mood

Step-by-step explanation:

An observational study is a study in which a researcher just records behavior in a particular manner without  interfering with the behavior.

In this study, the researcher has no influence or control over the variables .

From the given options , only option A representing a situation which can be an example of observational study."Placing different groups of people in different colored rooms and recording their mood "

Here the researcher just recording the mood of people without any influence.

the equation cos(35) =a/25 can be used to find the length of bc what is the length of bc? round to the nearest tenth

step-by-step explanation: