【正确答案】正确答案：The sense relation of(a)is synonymy. The two words "casual" and "informal" have similar meaning. One more example of synonym; "buy" and "purchase". (b)is a pair of antonym. The two words have opposite meaning. There are three main subtype for antonymy, namely gradable antonymy, complementary antonymy and converse antony-my.(b)is the first type. Another example for antonymy; "good" and "bad". "Steal" and "steel" are a pair of homonym, which have the same pronunciation but different meanings. One more example for "homonym" ; "no" and "know". "Animal" and "dog" have a sense relation of hyponymy, in which "animal" is a superordi-nate while "dog" a hyponym. One more example; "bird" and "lark".