I'm trying to find a regex to match the questions in a PDF textbook. The questions take the following structure:

1. What does cabotage refer to?
a. Domestic air services within a state
b. An international air carrier
c. A flight above territorial waters
d. Crop spraying
2. The Convention signed by the states relating to damage caused by foreign aircraft 
to persons and property on the ground is:
a. the Tokyo convention
b. the Rome convention
c. the Warsaw convention
d. the Paris convention.

I've tried modifying the one given here