I don't know the reason ________ the house is so dirty．

that

which

why

when

观察下列句子中的画线部分并将其译成汉语。

1．We thought you were a person from whom we could expect a good decision．

___________________

2．Do you remember the day when we left you in charge?

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3．This is not a family where bad behavior goes unpunished．

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4．I don’t know the reason why the house is so dirty．

___________________