In each of the following examples identify the population, the sample, and the research variable.
a. To determine the total amount of error in all students' bills, a large university selects 150 accounts for a special check of accuracy.
b. A wildlife biologist collects information on the sex of the 28 surviving California condors.
c. An organic chemist repeats the synthesis of a certain compound 5 times using the same procedure and each time determines the percentage of yield.
d. The Census Bureau distributes a special questionnaire to 1 out of every 20 households in the census and among other questions inquires about the number of rooms in the dwelling.
e. A manufacturer examines the records of each of its employees to determine how long each one has worked for the company.