Thoughts on the design:
本单元的Grammar主要讲的是现在分词，目的是让学生了解现在分词的用法。而本课时是Grammar的第一课时：现在分词可以作形容词和副词作用，在句中作定语，表语，宾语补足语。通过讲练结合的方式，由易到难，确保学生循序渐进地掌握语法内容。
Teaching aims:
After learning this section, the students will be able to
1. understand verb-ing form as adjective and adverb.
2. master a verb-ing form as attributive, predicative, object complement ect.
3. know how to apply the usages to practice.
