I don't know if he will come tomorrow.为什么要用if 不能用whether

I don't know if he ____(be) free tomorrow. I don't know if he ____ ( come ) I don't know if he will come tomorrow i think he if he free I don't know if he_.if he _home,please let me know.(return). I don't know if he ___.if he ____,please tell me .(come) I don't know if he will come tomorrow.为什么要用if 不能用whether i really don't know if he _____tomorrow.if he_____,please give me a ring(come) (w )if i don't know angone?括号里应该填什么? I don't know if Mr.Green_______(come) tomorrow,but I will let you know if he _____(come) tomorrow I don't know if he ___(come) tomorrow.If he ____(come),I'll tell him about it I don't know if he __ to the movie this evening.If he wants,so ___ I. I don't know （ w ） he will go there or not 英语翻译i don't know if i should i don't know if i should i don't know if i should i don't know if i should i don't know if i should i don't know if i should i don't know if i should i don't know if i should i don't know if i should i don't know I don't know what he needs i don't know if he comes next week哪里错了 I don't know if he is ( )class five.括号里填介词 I don’t know ___________ he is well or not.whether/if,为什么? I don't know if he ( ) If he ( ) .I'll let you know此题考的是什么 答案是will come ; comes为什么