代表样标签卡片的填写内容包括：井号、编号、井段、（）和挑样人。
A.岩性
B.电性
C.重量
D.井别
参考答案：A
如图，△ABC中，DE是AC的垂直平分线，AE=4cm，△ABD的周长为13cm，求△ABC的周长．
Mr. Smith graduated from college at the age of 23, and ___________ he has been working as a teacher in a middle school.
A．after that
B．from then on
C．from then
D．since then
