In the textbook notation for experimental design

Group of answer choices

a$.$ X represents control group respondents.

b$.$ X refers to the method employed to measure the response variable.

c$.$ O represents the exposure of a respondent to an experimental treatment.

d$.$ X represents the exposure of a group to an experiential treatment whose effect is to be observed, and O represents the observation or measurement taken on the group.

e$.$ O$1$ and O$2$ represent the matching of experimental and con