`1`. Because some fashion designers have printed lines of poetry on the "ao dai", it looks modern.
`2`. The "ao dai" has been mentioned in poems by poets for centuries.
`3`. The design and material used for men were not the same as those used for women.
`4`. My father hasn't smoked for two years.
`5`. Why don't we use electricity economically?
`6`. A whistle will be blown if there is an emergency.
`7`. They began working in that factory ten years ago.
`8`. He wishes he weren't late.
`9`. The soil here is said to be very rich.
`10`. Helen has been learning chinese since 2000.
