Why did portugal grant independence to its african colonies?

Because Africa began a nationalist movements.

Explanation:

The Portuguese were the last europeans to give up their African colonies.

Guinea did declare independence in 1973.

Cape verde islands declared national independence on 5 july 1975.

Sao tome  on 12 of july of 1975 declared its independence and angola was added to this on november 1975.

the answer is a) high entry costs