应选B.yet较委婉.现补充yet用法一、副词 yet 作“还”，“仍然”讲1. Much yet remains to be done. 尚有许多事情待做。2. Yet molecules are always moving, some perhaps as fast as a mile per second. 分子仍然总在运动，其中有些分子的运动速度达每秒一英里。3. The experiment is not yet over. 这项试验尚未结束。4. No one has yet seen an electron. 还没人见过电子。5. Man has not yet learned to store the sun's heat. 人类尚未学会贮藏太阳热。二、副词 yet 和比较级连用，作“还要”，“更”讲，常可用 even 代替1. This is a yet ( 或 even) more difficult task. 这是一项更为艰巨的任务。2. We must study yet ( 或 even) harder. 我们必须更加努力学习。 三、副词 yet 用于现在完成时作“已经”讲，只用于否定句和疑问句中1. Have you seen such a space shuttle yet? 你（已）见过这样的航天飞机吗？2. Has the bell rung yet? 铃已打过了吗？3. The bell has not been repaired yet. 铃尚未修好。注：在肯定句中表示“已经”要用 already，不能用 yet。若在疑问句中用 already 代替 yet，则表示惊异的语气。 eg: Has the bell rung already? 铃真的打过了吗？四、连词 yet 和 and yet, but yet 用法举例1. It is very good, yet ( 或 but) it can be better. 这很好，但还能精益求精。2. It is strange, and yet it is true. ( =It is strange yet ( 或 but) true.) 真奇怪，却是真的。3. Air has weight, and yet it is very light. 空气有重量，虽然很轻。4. Although this matter sounds strange, yet it is true. 此事听起来虽然奇怪，但却是事实。5. The wheel is the simplest yet ( 或 but) perhaps the most remarkable of all inventions. 轮子是所有发明中最简单却也许是最非凡的一种。6. Everyone thinks that this is a simple method, (but) yet he cannot believe it. 大家都认为只是个简单方法，但他不信。五、词组 as yet （到目前为止）和 just yet （就在此刻）常用于否定句中1. They have not made such an advanced computer as yet. 他们目前尚未制造出这样一种先进的计算机。2. No one has as yet been able to produce the absolute zero of temperature. 还没有人能产生绝对零度。3. It will not happen just yet. 此事一时尚不至于发生。
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