[填空题]
Estimate the observed wavelength forco9sq-:d+b/rw j 6vmh db)k;rp; 4mun(2rhvsiyo j91:/mi st the 656-nm line in the Balmer series of hydronktdm2 :94(sr mpy1;;ouihv )jir s/b gen in 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
