Complex sentence: Instead they can be created by two mechanisms: the first one is by gravitational lensing of E-modes, which has been measured by the South Pole Telescope in 2013; the second one is from gravitational waves arising from cosmic inflation.
Split into simpler sentences: Instead they can be sourced by two mechanisms: first one is by gravitational lensing of E-modes, which has been measured by the South Pole Telescope in 2013. Second one is from gravitational waves arising from cosmic inflation.