英文的2個問題

Yes, they have differences!!
For example:
A) City and citizens:
There are many citizens in this city.
City - the place in a country.
Citizens - the people live in the country.
B) Since and after
Examples:
1) Please do something for me SINCE you are free.
You cannot say "please do sth for me after u are free" (DOESN'T MAKE SENSE)
2) Please see me AFTER lunch.
cannot say "Please see me since lunch." (Also DOESNT MAKE SENSE)

city : 城巿/都市
citizens : 市民

since : 從...至今、因為、此後、由於
after : 之後、模仿、儘管、尋找

1.city=城市,都市,市
citizens=市民,(城市)居民

2.since=此後;從那時到現在
after=在...以後

city係城市,citizen係市民
since係此後或者從那時到現在,after係之後