Why did Portuguese attempt at assimilation fail

Portuguese attempt at assimilation failed because they did not try to educate their colonies enough.

Explanation:

Only Brazil is the nation where Portuguese is still spoken and some of the Portuguese culture has stayed as there is not much that the Portuguese were able to do in cultural assimilation despite having many colonies across the world at one point of time.

This was because they did not care much for education of theirs subjects and often treated them very harshly.

They were also not very willing to set up modern societies in their colonies and only were willing to profit.

letter d is correct.

it's no easy i swear it's hard