"I sindacati lo sanno."
Traduzione:The unions know it.
Just in order to share the personal experience with other guys here, let me tell you that my translation has been "The Unions know it" (exactly the same translation offered by Duolingo) only for one reason: to get the formal consent to go on. In effect, the translation I prefer is "The Unions know that"... Even if formally it is wrong ("that" in place of "it").