Mrs Collins and Mrs

Mrs. Collins and Mrs. Grey both administered the same IQ test to their regular classes by reading instructions, refraining from providing any verbal feedback, and generally following strict procedural guidelines. Even though the classes were comparable, Mrs. Grey's class had much lower test scores than Mrs. Collins. It is likely that

A) the instructions were not clear.
B) standard test administration does not work.
C) some subtle non-verbal cue or body language affected scores.
D) the race of the teachers affected test scores.