一．单项选择（共15小题；每题1分，满分15分）
从每题所给的A、B、C、D选项中，选出最佳选项。
( )1. He is only _______ boy. He isn’t old enough to take care of himself.
A. a 8-year-old B. a 8-years-old C. an 8-year-old
D. an 8-years-old
( )2. I remember Susan left _______ a very cold morning of January.
A. on B. in C. at D. from
( )3. He’s often heard ____ in the next door.
A. sing B. to sing C. singing D. sings
