Translation:Practice is important to learn Portuguese.
"in learning portuguese" should be accepted. I hate that this software is so strict on their english translation when the purpose is to learn portuguese. Duolingo - what a failure!
I know Duolingo has been going for some time, but you are still one of the early users of the Portuguese lessons. You can help out others who want to learn the language in the future by taking a moment to report the errors you see (or think you see) now.
The way they punish you for English 'mistakes' is ridiculous and off-putting. You should not need a Masters degree in English Grammar and Syntax just to learn basic Portuguese, children who can't even do their 3x tables are learning languages to fluency before high school.
I think they need a linguist to check over the Portuguese to English translation exercises.