[填空题]
Estimate the observed wavelength for the 656-nm line o mxqt:-erik;t 7unb iu+9anaf4m/ 64in the Balmer seri50nagciz/wrda/ i8 8k yk6;d xes of hydrogen ;ki8wcgz/x0kryd8 6 5 niaa/din the spectrum of a galaxy whose distance from us is
(a) $1.0 \times 10^6\ \text{ly}$, $\approx$ nm
(b) $1.0 \times 10^8\ \text{ly}$, $\approx$ nm
(c) $1.0 \times 10^{10}\ \text{ly}$. $\approx$ nm
