This is hilarious, what do the pictograms mean?
This sentence is a real treat in Timed Practice...
die sieben Tage einer Woche = the 7 days of "a" week or "the" week ?
I would say it doesn't matter here, because either way it refers to any week of the year, not a particular week. Strictly seen "einer Woche" is "of a week".
Yeah unfortunately it marks that as incorrect :(