Elcol, you had it correct in the first place, and answer 'A' is the one they're after.
Think about it: climbing towards 29,200ft, climb thrust set, 300 IAS, ROC 1000fpm (say), Mach no. increasing ... 0.76 ... 0.77 ... bingo! 0.78. If you maintain that pitch attitude and thrust, the Mach no. will increase, so to stop it doing that, you pitch up, and the ROC increases. For a while, anyway, until as you climb higher, it starts to decrease again.
They didn't ask anything about the TAS, did they? As always, RTFQ and KISS.
Artisan, I don't know what 'real aircraft' you fly, but I'd stick to sailing your yacht chum. My 'real aircraft' were the Boeing 707/720B, Boeing 737-200/300, Boeing 757, and MD DC-10-30, and that's what I observed to happen on all of them.
