[单选题]
When a beam of light (w2wo1 77:y)6ilymqnzl+kjd is avelength = 59 mkhf sy)u)m1+0 nm), originally traveling in air, enters a piece of glass (index of refrac ms+kh1)) uymftion 1.50), its frequency
A. increases by a factor of 1.50.
B. is reduced to 2/3 its original value.
C. is unaffected.
D. none of the given answers