The reformation movement was a retaliation against certain practices of the catholic church. which written work marked the beginning of the reformation?

The answer is the 95 Theses.  It contained criticisms leveled against the Catholic Church and focused on the practice of selling Indulgences.  Indulgences was a fee paid to the Church in exchange for salvation.  Apart from indulgences, it also attacked other teachings such Purgatory and the authority of the Pope.  He nailed this at the Church in Wittenburg and was willing to debate on the topic of selling indulgences.  Other literary developments that contributed to the Reformation was the translation of the Bible from Latin to German making it easier for common people to understand and develop their own understanding of God.