This DL course is 100% consistent on this matter.
The demonstrative adjective (here 'ta') can be translated as 'the' or as 'that/those', but not as 'this'. That point has been made over and over again by the authors in these discussion pages.
My point is, you CAN know: Here you can use 'the' or ''that' but not 'this'.
Well, it may not actually be wrong, but nobody actually says it in this context, at least in American English.
Usually in the sentence "X finishes", X must be a person or other animate being. If X is an inanimate object, one says "ends" instead of "finishes". So:
1. I finished the book.
2. The book ended suddenly.