Using the Example in the Text of a Participant Receiving

Using the example in the text of a participant receiving therapy while sitting in a bath of ice water, what would be the best denominator for calculating ?

A) the square root of MS_error
B) the square root of MS_error after removing effects due to the Ice condition and its interaction with treatment
C) the standard deviation of participants in the non-ice condition
D) the standard deviation of difference scores