In option A, the suffix -en is used in the transformation of nouns to adjectives, adding the meaning 'made up of'. For example, in "It was a golden opportunity for him", the adjective 'golden' modifies the noun 'opportunity', by saying that the opportunity was a valuable one. 'Goldful', 'goldous' and 'goldly' simply do not exist in the dictionary. They're not used in Standard English, hence options B, C and D are incorrect.