where is the main verb of this sentence? hey guys, please help me to understand this sentence! where is the main verb of this sentence, in your idea? ....the only barrier between brain and machine being the senses — sight, sound and touch — through which humans and devices interface.... Is it the being or interface? what are the original sentences that connected to each other by relative pronouns? BTW, the source of that is this text: From computers and scanners to multifarious mobile devices, an increasing number of humans spend much of their conscious lives interacting with the world through electronics, the only barrier between brain and machine being the senses — sight, sound and touch — through which humans and devices interface. thanks a lot.