1. 同义词替换。
如 scientist 和 researcher 之间的替换，disadvantage 和 drawback 的替换，sign和indication的替换。
2. 同义词组的替换。
如：keep to oneself 替换 be not friendly
3. 主动与被动的替换。
The passengers were rescued by boats and pleasure-craft 替换 Boats and pleasure-craft came to rescue the passengers.
4. 加减关系的替换。
如，某题原文为 The bottles made in most places contain about three-quarters new glass and the rest is recycled.
