第一恒磨牙的牙胚发生是在
A．胚胎第4个月
B．胚胎第4周
C．出生后第1年
D．出生后第4个月
E．出生后第8个月
参考答案：A
He accidentally ________ he had quarreled with his wife and then he hadn’t been home for a couple of weeks.[ ]
A．let out
B．took care
C．made sure
D．made out
叶片结构
