Strong form market efficiency states that the market incorporates all information in the stock price. Under strong form market efficiency, which of the followings is$/$are correct?

Each security in the market will have an annual rate of return equal to the risk$-$free rate.

II$)$ The price of any one security in that market will remain constant at its current level.

III$)$ Corporate insiders cannot earn excess returns by trading on their private information

a$.$ II and III

b$.$ III only

c$.$ I only

d$.$ II only