Not special for this particular exercise, but it is being confusing for me when most of the comments are complaining about losing hearts or how a certain phrase sounds more natural in english. English is a second language for me, too, so it's usually helpful. But repetitions of the same complaint on the same thread of comments makes one lose track of what one is here for, which is learning portuguese. Thank you all who's read my first and last complaint on a duolingo exercise.
I don't think that this translation "the granddaughter is thankful for the cake" is an accurate translation of the sense of the word "agradecer". From what I understand and according to my Collins dictionary "agradecer" is a verb implying an action of "to thank somebody for something". Therefore to translate this sentence as "the granddaughter gives thanks for the cake" should be accepted as this shows the action of giving thanks and not just the attitude of "being thankful", something which may or may not be expressed verbally.
I wrote “The granddaughter says thank you for the cake.” It was marked wrong and the correct answer suggested instead was the same except substituting “thanks” instead of “thank you”. If it is given as a correct answer to say “The granddaughter says thanks for the cake” then it should also be correct to say “The granddaughter says thank you for the cake.”