Why did you do that?
你为什么要这样做？
Why did you do that? 你为什么要这样做？ I have my own reason. 我自有道理。 How come? 为什么？（相当于why) What's she doing it for? 她做这件事是为什么？ Why would you do such a thing? 你为什么会做这种事情？
It may prove unworkable.
这可能是行不通的。
It may prove unworkable. 这可能行不通的。 But there still exists possibility. 但还是有可能行得通的。 It is impossible to say now. 现在该是不可能的。 That was not in the cards. 那是不可能的。 That's out of the question. 那是不可能的。 I think it's unlikely for a while. 我想暂时是不可能的。 That's not gonna happen. 那不会发生的。
