Answer:
C. randomization
Step-by-step explanation:
We are told that the study randomly selects participants in the study to sleep in either a dark room or a room with light. This means that randomization is part of the study.
20/10 as a mixed number:
20 ÷ 10 = 2.
10 goes into 20 two times. So 20/10 as a mixed number is a whole number: 2.
20/10 = 2