The article 'an' is used before words beginning with a vowel sound. In option C, 'hotel' is pronounced with a 'h' sound (aitch), which is a consonant sound, so it should be 'a hotel' not 'an hotel'. In British English, 'h' can be silent in some words, but 'hotel' is not one of them - it always takes 'a hotel'. Options A, B, and D correctly use 'an' before vowel sounds.