Rejecting the Null

A is “less than”, i.e. mathematically it is “<". C is “not greater than”, i.e. mathematically it is “<=" or "less than or equal to". If he believes that returns on Mondays are GREATER than on other days, he needs to find a null hypothesis than is the opposite (and reject that statement), i.e. returns on Mondays are “NOT greater than” (which includes the case where it can be “equal to” as well).