问题
选择题
James is ______ boy. [ ]
A. a 18-month-old
B. a 18 months old
C. an 18-month-old
D. an 18-months-old
答案
答案：C
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James is ______ boy. [ ]
A. a 18-month-old
B. a 18 months old
C. an 18-month-old
D. an 18-months-old
答案：C
，试计算水池的至少多深？（g取10 m/s2）