city; town

smog

serious, deep, heavy (topic), profound (change), weighty (matter)

seriousness

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

copies of a newspaper or magazine

division, divide, a part / section, bureau, department

division, bureau / school club / category

part / section / division / department / club

becoming more serious