数学功课(Math homework)
Reading 17:
http://www.youtube.com/watch?v=yCkEJ65Y8oM
http://www.youtube.com/watch?v=_wovm5GN2E4&feature=youtu.be
Reading 16:
Reading 15:
Reading 14:
Reading 9:
Reading 8:
Reading 7:
Reading 6:
Reading 5:
Reading4:
Reading 3 :
reading 2:
reading 1: