The key answer of exercise 3

a)

The text is about some of the most common myths about bilingualism.

b)

1. Danish, English, Portuguese, Spanish, Italian, German
2. Danish and English from his mother; Spanish from his father; Portuguese, Italian and German from living in countries where those languages are spoken.
3. around fifty percent
4. pronunciation
5. protection against mental illnesses such as Alzheimer's

c)

1. native
2. pick up (pick up something)
3. multilingual
4. persistent myths
5. acquire
6. gain insights