The correct option is B an
THE is the definite article. It signifies specific items. It is also used before words that have been mentioned previously in a given context. A is generally used before singular nouns which begin with a consonant. AN is usually used to introduce singular nouns that begin with a vowel. But, there are some obvious exceptions. In this case, 'h' is silent in honourable. So, when we pronounce the word honourable, the vowel sound 'o' is generated. That is why we have put 'an' before honourable and not 'a'.