a) & c) are correct! only b) & d) we need to look deep :
Actually, we are assuming here that LHS to be specific and trying to transform the same meaning to RHS. So in b) LHS specifically selects attribute A1 then applies condition C1 so interchanging them in RHS will do no harm.
But in d) we are keeping projections options open by applying first C1 then A1 but in RHS we are restricting by projecting only A1 then C1 so it's not safe.
For RHS in d) C1 may have been related to other attributes but since they will not be present then the query might return empty but in LHS we are keeping options and not restricting.
Thus answer d