Hi, Elena! In my opinion the second sentence is the best one, because "into" expresses a movement. “Into” can be used when we're talking about going towards the inside of a place. "In" can be used to say the place where someone or something is. Have a nice day!

Both are correct. Why? Because 'in' and 'into' mean the same thing. I could dissect the two words and find a difference but I don't feel that it's important in this case.

Both are correct and their meaning is the same... why? because in the first one you are saying implicitly "how does a person enter the car without the keys to open door?" and the word that you are using instead of that phrase is the word "in". For the second one is the same thing you use the word "into" instead of "in". I don't know if you know what am i saying... but if you have any question and you consider that i can help you ask, send me a message ok?