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気を使う， 気を遣う， きをつかう
1. to worry (about), to fuss (over), to be careful (about), to pay attention (to), to take (good) care of
担心(某事)，操心(某事)，小心(某事)，注意(某事)，照顾好...
に
1. at (place, time), in, on, during
2. to (direction, state), toward, into
3. for (purpose)
4. because of (reason), for, with
5. by, from
6. as (i.e. in the role of)
7. per, in, for, a (e.g. "once a month")
8. and, in addition to
9. if, although
tbd