If an advertiser adds affinity audiences and topics to the same targeting group, a TrueView ad will show:

A) only on targeted affinity audiences
B) only when targeted topics and affinity audiences match
C) on targeted topics and affinity audiences
D) only on targeted topics

The correct answer is:

C) on targeted topics and affinity audiences

Explanation: If we use affinity audience, the ad may be shown to the visitor, having immense interest in our product. In this case, the can be shown on the pages irrelevant to our keyword, because we are targeting the audience. The audience who has seen the relevant pages earlier and shown the interest to similar products. That is why they are being added to affinity audience. Now, when we target topics, the ad will be shown on the relevant pages. Because we are targeting topics, that are associated with a page.

Read more here (about the definitions only): https://support.google.com/partners/answer/2454017?hl=en