燃气管道的吹扫顺序是（）。
A.庭院管→支管→主管
B.主管→庭院管→支管
C.支管→主管→庭院管
D.主管→支管→庭院管
参考答案：D
Think and write. 想一想，照例子完成句子。
eg: That is Danny. That is his book.
That is Danny's book.
1. This is Jenny. This is her pencil.
2. That is Li Ming. That is his glue.
3. This is Mary. This is her chair.
A．I= ，从上向下
B．I= ，从上向下
C．I= ，从下向上
D．I= ，从下向上
