The correct answer is option C.
Register is the type of language used for a specific aim. It can be formal, informal or neutral. A letter to the movie theatre should be written in a quite formal register, which is usually used in professional situations and with people who are not close friends. It is characterized by elaborated and uncommon vocabulary, full words without contractions or abbreviations, as well as the use of complex sentences, passive voice, indirect questions and noun phrases.
