I.单项选择（共20小题，每小题1分，计20分）
选出可以填入空白处的最佳选项。
1. This term, we have ________ new subject—physics. It’s interesting.
A. a B. an C. the D. /
2. My sister is only four years old, but she can look after ________ now.
A. she B. her C. hers D. herself
3. I hear ________ students went to the hall to have the concert.
A. two hundred B. two hundreds C. hundred of D. two hundred of
