i. I'm not used to the noise yet.
ii. They used to work in a circus.
iii. Didn't there use to be a shop there?
iv. I never used to smoke.
v. It didn't use to be so dirty.
closed as too broad by Ivo Beckers, Deusovi♦, manshu, Gordon K, Raystafarian Feb 1 '16 at 18:38
Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
Maybe not the intended answer, but:
ii. They used to work in a circus.is the only one that does not use a negative.
I think it is
1. I'm not used to the noise yet.
in this phrase, "use" does not refer to something in the past (used to be), but to adaption (be used to).