Need advice on singular or plural form, thanks teachers

[Help Wanted]

Should I choose the singular or plural form in the brackets that follow? Please advise, thanks teachers.


Mobiles phones emit strong radiation. If we use (it or them) for too long, (it or they) may damage our (brain or brains).

There are a lot of reasons why teens should be prohibited from having (a mobile phone or mobile phones).

[Tdol]

Them/they/either/either

[Help Wanted]

Many thanks for your prompt advice, teacher Tdol!