One of the Absorption Lines of Hydrogen Has a Rest

Multiple Choice

One of the absorption lines of hydrogen has a rest wavelength of 656 nm (at rest means with respect to the observer, like in a lab) . You observe several stars and measure the wavelength of this same hydrogen absorption line in each star. Based on the measured wavelength of this line, which star is moving towards the Earth the fastest?

A) 640 nm
B) 670 nm
C) 656 nm
D) 630 nm
E) 680 nm