Upgrades can be to an area.Logical formLearned from8 sentences. Upgrades can be to an engine.Logical formLearned from8 sentences. An upgrade can be compatible.Logical formLearned from8 sentences. Upgrades can be to a stadium.Logical formLearned from8 sentences. Conjunction can be with an upgrade.Logical formLearned from8 sentences. An upgrade may pertain-to airports.Logical formLearned from8 sentences. A station may undergo an upgrade.Logical formLearned from8 sentences. An upgrade can be from previous versions.Logical formLearned from8 sentences. An upgrade can be for systems.Logical formLearned from8 sentences. Factors may affect an upgrade.Logical formLearned from8 sentences. (Network upgrades) can be costly.Logical formLearned from8 sentences. An upgrade can be inevitable.Logical formLearned from8 sentences. Upgrades can be selected.Logical formLearned from8 sentences. Upgrades can be in hardware.Logical formLearned from8 sentences. An upgrade can be from a company.Logical formLearned from8 sentences.