Hello Siqi Zang, The reason to use that tense in the first sentence is the same one in English. You would say "would have done", right? So that is why you use it in Spanish. The rule we are following there is none other than to express something want to change but in the past. On the other hand, you use the imperfect tense in subjuntive mode in the second sentence because that action was being continued in the past. Regards, Alfonso

1) Te dije que lo ______ (hacer) yo mismo. Answer: hubiera hecho 【Why here I need to use 'el subjuntivo pluscuamperfecto'?】 You need to use subjuntivo pluscuamperfecto because this is the tense of "regrets". We use it everytime we reimagine the past. This is called the third conditional (the impossible one). We can´t change the past, but we can imagine and say what would have been. In Spanish we need pluscuamperfecto to express this. Actually, this sentence could also be: Te dije que lo haría yo mismo (conditional). It really is a matter of perspective. If you say, te dije que lo hubiera hecho yo mismo, you´re probably implying that in the past you said it was better if you do it but then someone else did and it didn´t turn out the way you expected so you say: I would have done it myself, as I told you (it would have been better that way) 2) Te lo conté para que lo ______(saber). Answer: supieras 【Why here I need to use 'el subjuntivo imperfecto'? I know that after 'para que' I should use 'el subjuntivo', but why 'imperfecto'?】 Again you have two options: Para que lo sepas/ para que lo supieras. And it is a matter of perspective as well. I´ll give you an example with a different verb. Lo cociné para que lo comas vs Lo cociné para que lo comieras Subjuntivo presente expresses a type of future (more like an intermediate space between present and future), so maybe I´m in the kitchen with my husband telling him that I cooked it so that he eats it (in a moment, in a few minutes or in some hours). Imperfecto del subjuntivo expresses what the purpose WAS. So, If I say, para que lo comieras, and I´m in the kitchen with my husband I probably mean from my perspective that he hasn´t eaten it yet but I´m explaining that I cooked it for him and that I expected him to have eaten it already. Your question is linked to the three types of conditional sentences in Spanish. I hope this answers your question and please feel free to contact me if I can help you more.