【正确答案】(a)Casual and informal are synonyms. Example: buy—purchase.
(b)Intelligent and stupid are antonyms with opposite meanings. Example: tall—short.
(c)Steal and steel are homonyms, having the same pronunciation but different meanings. Example: air—heir.
(d)The sense relation between animal and dog is hyponymy. Animal is the SUPERORDINATE of dog, which is called HYPONYM. Example: bird—sparrow.

【答案解析】[解析] 此题考查的是考生对语义关系的理解。语义关系主要包括：同义关系、反义关系、上下义关系、同音/形异义关系等。考生应掌握各种语义关系的含义并能举例分析。