It is the official source. It includes not just the answer keys, but also transcripts for all audio tracks and additional interactive exercises.
For every mistake, ask yourself: Was it a conjugation error? A preposition slip-up? Or a vocabulary misunderstanding? Key Topics Covered in Aula Internacional Plus 3 3 aula internacional plus answer key
When checking your answers, pay extra attention to these "heavy hitter" topics in the B1 level: It is the official source
Alternatively you can download TextDiff from the Microsoft Store. Please note that if you do, Microsoft will provide the software, process the payment and provide the licensing system. If you have installed the software from this website, you will need to download the software again from Microsoft. You need Windows 10 version 15063 or higher if you choose to download this software from Microsoft.