- 17 The future tense _ The parts of speech _ Grammar _ Khan Academy 视频 0 次下载
- 18 Helping verbs _ The parts of speech _ Grammar _ Khan Academy 视频 0 次下载
- 20 Introduction to irregular verbs _ The parts of speech _ Grammar _ Khan Academy 视频 0 次下载
- 21 The funky -ed irregular verb _ The parts of speech _ Grammar _ Khan Academy 视频 0 次下载
- 22 The vowel-shift irregular verb _ The parts of speech _ Grammar _ Khan Academy 视频 0 次下载