英语四级六级阅读练习（19）：灰尘背后的那些事儿

1. Generally, the majority of household dust — about 60% — comes from outside, through windows, doors, vents and on the soles ofour shoes.

2. Lead loading on floors.

3. It's important that you try, just clean regularly, don't smoke, eat at the table — and try not to freak out.