The correct options are B) Age
C) Which people were selected for the sample
D) The amount of coffee consumed
Explanation:
A hidden variable can be described as a variable which is not under study but might be a reason for the occurrence of changes in the dependent variable.
For example, the consumption of coffee is the independent variable which cause cancer ( dependent variable). However, there might be certain other factors such as the age, type of people being selected for experiment which might have resulted in the occurrence of the dependent variable but remain hidden.