Which fact do dual frequency receivers use in estimating the ionospheric effect? O The propagation speed through the ionosphere is the same for each carrier frequency O The receiver clock error is...

Please explain.

Extracted text: Which fact do dual frequency receivers use in estimating the ionospheric effect? O The propagation speed through the ionosphere is the same for each carrier frequency O The receiver clock error is smaller for dual frequency receivers O The ionosphere is a dispersive medium. O The satellite clock bias is smaller for dual frequency receivers