The one$-$month stock return reversal phenomenon states that the

performance of an individual stock in the past month tends to predict its

performance over the next month in the opposite direction. If this

phenomenon were a result of irrational investor behavior and it generates

a true abnormal return, which of the following forms of capital market

efficiency is violated? Choose the most appropriate answer.

a$.$ Weak form efficiency

b$.$ Semi$-$strong form efficiency

c$.$ Strong form efficiency

d$.$ Mean$-$variance efficiency