二氧化硫是污染大气的主要有害物质之一，下列可以作为其污染程度指示植物的是[ ]
A．苔藓
B．铁线蕨
C．水绵
D．卷柏
A
根据汉语提示填入适当的单词。
1. I think the calculator was _____ (发明) before the computer.
2. A stamp is used for _____ (寄) a letter.
3. Shoes with adjustable heels are used for _____ (改变) the style of the shoes?
4. What do you think is the most _____ (有用的) invention
5. I'm sorry I took your book by _____ (错误).
成人十二指肠 * * 在十二指肠降部后内侧壁约距幽门
A．7cm
B．8cm
C．9cm
D．10cm
