Why are the 1300 nm and 1550 nm regions of the fiber spectrum primarily used for optical communications？（）

• A、 They are both regions of lowest loss.
• B、 They are both regions of low reflections.
• C、 They are both regions of low index of refraction.
• D、 They are both regions of low chromatic dispersion.
• E、 They are both regions of low Polarization Mode Dispersion （PMD）.