Hello. Please revise my sentences
1. I was sitting on my own.
2. It has a lurking sense.
3. He wants to organize a knees-up.
4. The temperature was getting decline.

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Answer

#1 is good, you could also say "I was sitting by myself".
#2 "It was lurking." or "It had a sense of foreboding" - I think that fits the general meaning?
#3 "He wants to organize a meet-up." This is the only thing I can imagine "knees-up" means, I've never heard this before...
#4 "The temperature was declining." or also "The temperature was falling." The last one is probably more natural. Pretty close on this one though :)

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Agree with all of the above, but for #4 I would say "It's getting colder outside."