Present simple or present continuous?

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?

Solution 1:

If it were boats, you could definitely say

Pat has got an interesting hobby. She builds boats.

However, because it's about a particular boat, you cannot build it over and over again, hence the simple present (which implies regularity, recurrence) is not very appropriate.

The present continuous, on the other hand, is not necessarily used for actions that are literally taking place at the moment of speaking. You can say

I am reading "Moby Dick".

without having the book in your hands at the moment of the utterance. Building a boat is a long process. Even though it is not necessarily uninterrupted, it is still a continuous action, hence the continuous tense should be used:

Pat has got an interesting hobby. She is building a boat.