What Is the Meaning of Counterbalancing

What is the meaning of counterbalancing?

A) Counterbalancing is an experimental technique in which all possible orders of presenting the variables are included
B) Counterbalancing is an experimental technique in which all possible orders of presenting the variables are not included
C) Counterbalancing is an experimental technique in which some possible orders of presenting the variables are included
D) Counterbalancing is an experimental technique in which some possible orders of presenting the variables are not included
E) Counterbalancing is an experimental technique used in between-groups designs to ensure unbiased allocation of participants to conditions