"Yo no tengo fuerzas."
I think there is an error here. When I hovered the new word, fuerzas, it defined it as (you) force, (you) strain.... The words ¨strength¨ and ¨energy¨ were not to be found, even in the Explain button. I´m guessing fuerzar is also a verb?
OK, thanks. I wondered if it might be something like that. Perhaps the hover-help should reflect this (as it did correctly for "por favor"). This was my first time seeing the word/expression, and when I used what it indicated, I was pronounced wrong.