Which TV network originally aired 'The X-Files'?

Which TV network originally aired 'Cheers'? Which TV network originally aired 'I Love Lucy'? Which TV network originally aired 'M*A*S*H'? Which TV network originally aired 'Lost'? Which TV network originally aired 'South Park'? Which TV network originally aired 'Sex and the City'? Which TV network originally aired 'Dexter'? Which TV network originally aired 'It's Always Sunny in Philadelphia'?