proč jsou v nabídce každé věty vždy přesně 4 slova navíc, takhle se s tim dá počítat a dost to usnadňuje její složení
It is true that most word bank exercises contain exactly four extra words. (This has helped me more than once when I had five words left over.) Some have no extra words at all but I don't remember seeing one, two, three, or five.
This applies to the browser version; in the mobile app, fewer than four extra words seem to be not uncommon.