...careful not to wake everyone up

He tiptoed along the corridor, careful not to wake everyone up.

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If I want to add a conjunction to the sentence above, which meaning of the following sentence is more close to it?

1. He tiptoed along the corridor, and he was careful not to wake everyone up.
2. He tiptoed along the corridor, because he was careful not to wake everyone up.
3. He tiptoed along the corridor, as he was careful not to wake everyone up.
4. He tiptoed along the corridor, as if/though he was careful not to wake everyone up.
5. (Maybe you have a better answer.)

Would you be so kind as to help me?
Thanks!

PS I also posted the same question on https://goo.gl/hGuzkV, but all of your answers are unique to me. Hope we can discuss with each other. Thank you.