Usage of a été and était

Question

I don't understand the usage of a été and était in some cases.

For example, in this exercise: https://kwiziq.learnfrenchwithalexa.com/my-languages/french/exercises/overview/1414
one of the sentences is "Ce matin j'ai été assez paresseuse". Why is "j'ai été" used here instead of "j'étais"? Doesn't "ce matin" automatically imply duration (as in she was being lazy the whole morning or during some part of the morning)?

But in this exercise: https://kwiziq.learnfrenchwithalexa.com/my-languages/french/exercises/overview/1414
one of the sentences is "Maman était très heureuse". Why is it "était" instead of "a été"?

Jim Jones · Accepted Answer

Bonjour V.B.
 "Ce matin j'ai été assez paresseuse"
This is a completed action that took place at a particular time of the day, being reported as a reflection of then, but at a later time. Passé composé
 "Maman était très heureuse"
This is a "state of mind" or human emotion that is an incomplete situation, enduring.
The imperfect is therefore appropriate in this case  --  not a completed action. 
I hope this helps to clarify the two cases for you.
Bonne continuation
Jim