Use the present simple or the future simple. i dont know when my elder brither(come)back home.if he (come) after eight,he (miss) his favorite tv show.when jack (return),he (help) us; but i don't know yet when he (come) back.if the ecological situation (improve),people (feel) much better; but we still don't know when it (happen).he (not,tell) you anything if you (not,ask); but im not sure (stop) raining at all today.
