【正确答案】：
ANTONYMS ARE USEFUL IN ENABLING US TO EXPRESS ECONOMICALLY THE OPPOSITE OF A PARTICULAR THOUGHT, OFTEN FOR THE SAKE OF CONTRAST. MANY IDIOMS ARE FORMED WITH ANTONYMS. GROUP (A) IS SUCH AN EXAMPLE, THESE IDIOMS LOOK NEAT AND PLEASANT, AND SOUND RHYTHMIC. 
ANTONYMS ARE OFTEN USED TO FORM ANTITHESIS TO ACHIEVE EMPHASIS BY PUTTING CONTRASTING IDEAS TOGETHER. PROVERBS AND SAYINGS PROVIDE US WITH GOOD EXAMPLES, SUCH AS EXAMPLES IN GROUP(B).
【题目解析】：反义词有助于我们简练地表达某一特定思想的对立面，这经常是为了对比的需要。许多成语是由反义词构成的。Group (a)就是这样的例子，这些习语看起来整齐、赏心悦目、富有节奏。为了强调，反义词常常通过将对立的思想拼合在一起形成对偶，谚语和名言为我们提供了很好的例子，Group (b)就是这样的例子。