Complex sentence: The Silence's origins are given in "The Time of the Doctor" (2013) that they genetically modified priests belonging to the Church of the Papal Mainframe; sinners forgetting confession immediately after giving it.
Split into simpler sentences: The Silence's origins are given in "The Time of the Doctor" (2013). They are genetically modified priests belonging to the Church of the Papal Mainframe; sinners forget confession immediately after giving it.