One Way of Providing Some Control in a Causal-Comparative Research

One way of providing some control in a causal-comparative research design is to:

A) match the subjects in the groups to be compared on as many extraneous variables as possible
B) list all of the subjects from the population under study and randomly assign them to experimental and control groups
C) do a pilot study before carrying out the main research
D) obtain measurements on an additional dependent variable