The two ways of relating what a person has said are 1)direct and 2)indirect (reported speech).In direct speech, the original speaker's exact words are repeated. In indirect/reported speech, the exact meaning is expressed but not necessarily using the original speaker's exact words. Pronouns and possessive adjectives usually change from first or second person to the third person except when the speaker is reporting his own words. Sometimes a noun can be inserted to avoid doubt.

When we turn direct questions and exclamations into indirect speech, they are converted to affirmative statement .( ? and ! is not used).

Option C is correct as when we convert the given direct speech to indirect speech, can't is changed to could, I to he, simple present tense to simple past tense (wasn't), the introductory verb advised is used (try), to is added and to which is used to connect the two dialogues.

 The other options are wrong as I, can't, and tried can't be used.

The correct answer is C)Sam told Sue that he couldn't open the door as the key wasn't turning to which Sue advised him to try it the other way.