The Procedure for Using Block Randomization in an Independent Groups

The procedure for using block randomization in an independent groups experiment with three conditions (A,B,C) and 60 subjects is to

A) generate twenty random orders of the conditions (e.g.,ACB,BAC) and assign subjects one block at a time (i.e.,3 subjects in the first block,3 in the second block,and so on) .
B) generate one random order of conditions (e.g.,ACB) and test the first 20 subjects in condition A,the second 20 subjects in condition C,and the last 20 subjects in condition B.
C) select intact groups of 20 subjects each and randomly assign the groups to condition A,B,or C.
D) generate sixty random orders of the conditions,one for each subject.