The article 'an' is used when the noun is known only to the speaker, it is an indefinite noun, and it begins with a vowel/vowel sound. Hence Option B is correct. 'A' is used for the same reasons as 'an', the only difference being that the noun starts with a consonant, hence option A is incorrect. Option C is used for a noun which has been mentioned before since it hasn't been mentioned before in the given statement, it's incorrect. Since an article is required for the reasons that are mentioned earlier and we are not referring to the insurance company generally, option D is also incorrect as we need an article in the given context.