I don't know 主句的“我不知道” 就使從句附上了不確定的（uncertain) 的意思, 故用if/ whether

I don't know if he he will go to japan next week.

【希望幫助到你,若有疑問(wèn),可以追問(wèn)~~~
祝你學(xué)習(xí)進(jìn)步,更上一層樓!(*^__^*)】那he is a student也用i don't know,變賓語(yǔ)從句，為什么他就是＋that?如果用 i don't know that he is a student. "我不知道他是個(gè)學(xué)生（這個(gè)事實(shí)）” 我不太認(rèn)同這個(gè)說(shuō)法。因?yàn)椋绻阏f(shuō)話的時(shí)候已經(jīng)知道他是個(gè)學(xué)生了，要說(shuō)不知道，那是過(guò)去的事i didn't know he was a student.再如：我不知道你在這。I didn't know you were here. (說(shuō)話的時(shí)候應(yīng)該知道對(duì)方在這了）