Greek, firstly because Egypt was owned by Greece under Alexander the Great, and secondly though not unrelatedly Greek was the official language of the Coptic Church.. Arabic, because they conquered Egypt and enforced Arabic as the spoken language. Sumerian, because Sumerian predated Egypt and had a heavy influence on Egyptian culture and language.

Under Alexander the Great, Greek became the lingua franca of the western world. Later, when Egypt adopted Christianity (really Byzantine Orthodoxy, as opposed to Roman Catholicism, which split and distinction are more convoluted than the British Monarchy), the resulting Egyptian Church adopted Greek as its liturgical language. As for the other options: The Muslim Conquest occurred in 642 A.D., after which Coptic fell into disuse. So, Arabic replaced Coptic rather than altering it. and... Sumeria did not predate Egypt, nor did it have a notable influence on Egyltian culture and language. Even if it had, this would have been an influence on Old Egyptian, not Coptic, which two stages are seperated by 3 to 4 millennia.