$10.$ State variables, decision variables, decision criteria and optimal strategy can be determined $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$ of a dynamic programming problem.

a$)$ only for phase $1$

b$)$ for phases $1$ and $2$

c$)$ for phase n $-1$

d$)$ for each phase.

e$)$ only for the last stage.