The question above has multiple choices as follows.
a. You can actually track any custom event you want to define.
b. All app installs and all in-app purchases
c. Android app downloads and Android in-app purchases
d. App installs and core user demographics
The correct answer is (C) Android app downloads and Android in-app purchases
You can automatically track android in-app purchases from Google play when someone who clicked your ad makes a purchase. There is no need of adding code to your app. The same concept works on Android app downloads.