Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2016 / S2 / 3 / c

After foreground and dipole removal, primordial CMB anisotropies are small hot and cold patches across the sky, with characteristic correlated angular scales and amplitudes of order $10^{-5}$ of the mean temperature. They trace perturbations at photon decoupling and subsequent propagation, not simply the current distribution of Milky Way dust.