句子的连贯指的是句子中各成分之间的关系明白清楚，富有条理。句子的不连贯表现为句子结构不平行，指代模糊，时态、语态、人称和数混乱等等。
原句：Not so many years ago in this city,one of the rivers was so polluted that there is no living fish in it.
优化：Not so many years ago in this city,one of the rivers was so polluted that there was no living fish in it.


原句：We know that violent crime is increasing,and you also know many incidents go unreported.
优化：We know that violent crime is increasing,and we also know many incidents go unreported.


原句：Both of the puppies is cute in their own ways.
优化：Both of the puppies are cute in their own ways.