正常小儿的头围与胸围大致相等的年 (月)龄是( )。
A.出生时B.6个月时C.1岁时D.2岁时E.3岁时
参考答案:C
解析:[考点] 小儿体格生长[重点等级] ★★★★★
"Mr. Smith is ill in hospital." "_____." [ ]
A. I'm sorry to hear that
B. Yes, he has to see the doctor
C. Don't worry about it
D. I'm glad to hear that
在阶跃型光纤中,数值孔径越大光纤性能越好。