Here is an exercise from Intermediate Language Practice by Michael Vince:
Complete the following sentence with a present simple or present continuous form of the words in bold.
Pat has got an interesting hobby. __________ a boat. she build
The answer key says "She's building", but I think "She builds" is more appropriate. As I understand it, the present continuous generally indicates a temporary situation whereas the present simple indicates a more permanent one. Without any more context, I see a hobby as a fairly permanent activity, so the present simple should be used here.
Is the answer key incorrect or am I missing something?