Martin Luther opposed the belief that salvation was dependent on faith and works, as he argued for justification by faith alone (sola fide). However, he did not oppose the core belief that salvation was dependent on faith itself.
Among the options given, he opposed challenges to the Church's authority, particularly the authority of the Pope and the sale of indulgences. He also opposed the refusal by the Church to practice the holy sacraments in a way that he believed was faithful to scripture.
From the choices provided, the most accurate answer would be challenges to the Church's authority, as Luther's actions were fundamentally about reforming the Church rather than completely rejecting its authority in a general sense.
If you mean to focus solely on what he directly opposed, then he would be considered at odds with issues regarding the corrupt practices within the Church rather than the Church's sacraments themselves.