This is a paraphrasing task. In this task, you're given a sentence and your task is to generate another sentence which express same meaning as the input using different words.
One example is below.
Q: Giraffes like Acacia leaves and hay, and they can consume 75 pounds of food a day.
A: A giraffe can eat up to 75 pounds of Acacia leaves and hay daily.
Rationale: Input and output sentence have same meaning in different words.
Q: it explained how a dozen robots could follow when one robot had been summoned , but only when needed and not otherwise .
A:
it could also explain why one robot was called upon when a robot was called , a dozen - but only when they needed to be .