=> I don't know.
2)It's just a quirk of the language.
=> 'quirk' means peculiar feature; e.g., though and doubt share the same vowel letters 'ou' but it's pronounced differently.
3)He's been involved in quite a lot of questionable deals.
=> 'questionable' means doubtful as regards the truth, honesty, quality, wisdom.
4)They have got serious cash-flow problems.
=> The lack funds/money; i.e., the money isn't flowing
5) I‘ll give up a little if the other person gives up a little.
6)I'm with you on that.
=> I agree
7) I think I'm out of the running.
=> I am no longer a competitor.
8)Carpe Diem with this.
=> Seize the day with whatever 'this' refers to.
9)They're a kind of cradle for the elite.
=> a 'cradle' is a safe, nurturing place.
Student or Learner