Which is the subject (and what's the other thing called)? is a crappy question.
In its entirety:
If I say:
My sister can drive the car today
Which is the subject: sister or car? Also, what is the other thing called?
This might be marginally interesting because of the can, but it shows absolutely no research. "The other thing?" There is more than one "other thing." That makes it unclear.
ELL is not a garbage can. There is a close reason on ELL that states:
This question should include more details than have been provided here. Please edit to add the research you have done in your efforts to answer the question, or provide more context. See: Details, Please.
Listed among the details are Explain why you are confused and Show your research.
The above question does neither. There have been other questions I've voted to close for the 'show your research' reason which I've seen others have voted to close in order to migrate to ELL.
Please treat ELL with the same respect that ELU should be accorded.
Granted I suffer from native English-speaker guilt, but every time I vote to migrate, I go over to ELL and answer a reasonable but unanswered question. That's how I deal with (my) karma. Maybe the people migrating crappy questions should think about doing the same; it might make them think twice.
Edited to add: I didn't know this question had such a nice, helpful answer, which is great when that happens. However, it is still a crappy question. What I have learned since then is that there has been some discussion on ELL about migrating crap, so maybe if the mods can let us know what they want (there is some disagreement), I can get down from this soap box. I'm old, and my balance isn't so good.