填空:平面图形中的线段可分为已知线段、____和连接线段三种。

A. To ask for a leave.
B. To ask for help on how to improve writing.
C. To show his outline to the professor.
D. To talk about college life.

A. He has recited enough words and expressions, but he doesn't know how to get started.
B. He has read a lot, but he doesn't know how to recite the new words and expressions.
C. He doesn't know what to write and how to write.
D. He can not understand what the professor taught him.

A. He taught him some shortcuts to improve writing rapidly.
B. He showed him methods on how to recite new words and expressions.
C. He taught the student how to write an outline.
D. He told the student to read more and write more.