Distribution of content items provided by content producer computers to content consumer computers via a computer network is controlled and indications of different interactions with content items contained in messages distributed to content consumer computers are tracked. The microwave frequency tunable filtering balun comprises a first microwave split ring transmission line resonator and a second microwave split ring transmission line resonator arranged in a bilaterally symmetrical manner, a fourth variable capacitor and a fifth variable capacitor of same parameters. By use of the dibenzoc,gcarbazole compound, a light-emitting element having very good characteristics can be obtained. The semiconductive material sidewalls of the gate line are oxidized.