Not the prime purpose of the lesson - but in the examples, why is 'you have been lying' the English translation of «tu as menti» (passé composé) rather than tu mentais (imparfait)? If the English translation was  'you lied' I would understand, as that implies an episode that is finished, but in English 'you have been lying' leaves open ' for a long time' and 'and you still are' scenarios - that is the sense that it could be ongoing and it is unclear when it started. The translation has me questioning (again) what further I need to understand to grasp the nuances of this past tense distinction.