"You told us to assume."
Μετάφραση:Μας είπες να υποθέσουμε.
"Assume" needs an object, it cannot stand alone, we assume our responsibility, we assume that you are correct, we assume that all will be well.
Assume with an object is correct. The problem for Duo is to introduce new vocabulary in very simple sentences, sometimes this means the sentence or phrase does not make sense but you do learn the word "assume" which is the main aim. So it is a compromise.