题干
.—Mum , I have finished my homework while you were out.
--_____a good boy.
A：It’
B：How
C：This i
D：That’
答案(点此获取答案解析）
D
A：It’
B：How
C：This i
D：That’
的前
项和为
，若
，则
（ ）
