[填空题]
Estimate the observed wavelength for,qjvfslii9 ph3y9g v/6v */ sd the 656-nm line in the Balmer serid xwjdeg9;t )06ih7pces of hydrogen in the spectrum of a galaxy whose tw gcd;07dxhi6p) je9distance 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
