牙萌出延迟的判断指标是（）
A.＞4个月
B.＞6个月
C.＞10个月
D.＞13个月
E.＞15个月
参考答案：D
用简便方法计算下面各题．
（1）1500-28-272
（2）99×48+48
（3）2000÷125÷8
（4）77+2.14+23+7.86．
---Emma has to stay at home to look after her little sister, ?
---Yes, because her mother has gone to the supermarket.
A．does she
B．is she
C．doesn’t she
D．hasn’t she
