请从A、B、C、D四个选项中选出可以填入空白处的最佳选项。
（ ）16. —Do you know Taiwan, Jenny?
— Yes, of course. Taiwan is _________ island in China.
A. a B. an C. the D. 不填
（ ）17. — Is your brother afraid of the dark?
— Yes. He always goes to sleep with the bedroom light _________.
A. off B. on C. in D. at
（ ）18. —How do you study English?
—By ________ the teacher for help.
A. asking B. invite C. find D. seeing
