選擇正確的引導詞補全句子
1.I don't know ________ he will come.(that,if)
2.I believe ________ he is a good teacher.(that,if)
3.I want to know ________ you join this club.(why,what)
4.They asked ________ I came from.(if,where)
5.I can't remember ________ I bought this bag.(when,that)