In Which Situation Might You Observe the "Allegiance Effect" in a Double-Blind

In which situation might you observe the "allegiance effect" in a double-blind study?

A) The researcher tries to replicate the results of an earlier study.
B) A treatment doesn't seem to be working, so the researcher puts less effort into that treatment group.
C) The participants in the treatment group show a greater commitment to the study than do participants in the control group.
D) The researcher and the participants in the control group work together to bring about a treatment effect.