sorry if wrong ;)
Teenager delinquency, in which (C) people are now complaining has become a popular topic discussed among psychologist.
'in which' is chosen as teenager delinquency is a phenomena, so can be considered as object (abstract one) or stuff, so 'which' is the suitable pronoun for it. The other words that can also be used in this is 'that'.
More example on relative pronoun is available on the link below
Kategori: relative pronoun
basically, itu nanyain tentang tabel kadarluarsa product nya kapan
a. will- use
s.present future tense
s + will/shal+v1 + ob