光是一种电磁波，当电磁波在空气中传播时，传播的速度是______m/s，红光的频率比紫光低，则红光的波长比紫光______（长/短/相等）．

"______" means "to have, show confidence or pride in one’s worth, good character, ability, .etc".

A. To ride one’s high horse



B. To keep a straight face
C. Not to bat an eyelid



D. To hold one’s head high