The correct option is D a; a; the
As per the rules of use of the indefinite article, the indefinite article is used in its original numerical sense of one i.e. to denote that there is a single unit of anything the indefinite article can be used to replace the use of number 'one'. Here since there are two paintings one black and one gold, the indefinite article 'a' or 'an' should be used before each noun in place of number one to denote a single unit of each. ‘A’ is used for nouns the sound of which begins with a consonant. Since it is a specific museum, the definite article 'the' should be used before it. Therefore Option D is the correct answer. Since 'the' cannot be used in place of number one, it cannot be used for the paintings and 'a' cannot be used before any specified thing so it cannot be used before the museum in this sentence. Therefore, Option A, C, and D are incorrect.