Today I was asked a question by a learner of german as a second language, to which I couldn’t find any useful answer.
We were reading the sentence „Sie müssen realisieren, mit welcher Herausforderung Sie es zu tun haben“. The learner did ask if and why the „es“ was necessary. I answered based on my intuition that leaving out the „es“ would seem somewhat wrong. But I couldn’t answer with certainty and was completely unable to explain the usage that this „es“ had in the given sentence.
I hope there are some grammar experts here, that can help me to give a more fulfilling answer to my friend.
Thanks in advance