Which of the Following Is TRUE

Which of the following is TRUE?

A) When it is not possible to go back after an experiment and determine if the experimental and control groups were equal before the fact, selection bias may be present in the experiment.
B) Matching is the preferred procedure to ensure equality of comparison groups.
C) To avoid selection bias, the general principle is: select subjects at random and then arbitrarily assign subjects to groups.
D) The use of randomization to eliminate selection bias in experimental designs works best when the groups being compared are small.
E) They are all false.