My teacher gave interesting assignments and motivating the students.
非常显然，这是混用语法结构的一个典型错误。这会使句子产生歧义：难道是说My teacher gave interesting and motivating assignments to the students? 由于本句中 interesting和motivating 是平行结构. 或者是My teacher gave interesting assignments and motivated the students? 由于亦可以理解成gave和 motivated是平行结构.所以错误用语法会带来很多意料之外的麻烦。
My teacher wrote the assignment on the chalkboard. The assignment was on the chalkboard until the teacher erased the assignment after we had all done the assignment.事实上这句话的看法会愈加明确，假如大家将重复的词替换为其他表达的话。大家再来看看改进后的表达：
My teacher wrote the assignment on the chalkboard. She erased the board after we had all completed the task.
其中 assignment 被替换为 task; teacher 变为了she; chalkboard 被改为了board. 不但句子看上去愈加生动活泼不刻板，信息量也比原来要多了。