题目内容

城市燃气管网按不同的压力级制数量进行分类，可分为四类，下列是错误的选项是()

A. 一级管网系统
B. 二级管网系统
C. 三级管网系统
D. 四级管网系统

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根据下列短文，回答下列各题。 A panel of government officials is worried．The air quality in

A. scientists
B. homeowners
C. citizens
D. factory owners

答案为：

A. to work
B. working
C. to working
D. work

答案为：

A. when
B. where
C. what
D. wherever

The author suggests that you purchase table linens made of________．

A. bleach-safe fabric
B. preshrunk cloth
C. easy-care material
D. stain-resistant coRon