搜索
Long ago, as people got older, there was something wrong with their teeth and it would be very painful.1．
Later people learned that cleaning their teeth was important, but they didn't have toothpaste(牙膏) at that time. 2．
About 100 years ago someone finally created a kind of cream to clean teeth. Not long after that, the toothpaste tube (管子) was invented, so people could press the toothpaste right onto the toothbrush! 3． The army gave brushes and toothpaste to all the soldiers, and they learned to brush teeth twice a day. At that time toothpaste tubes were made of metal. 4．
Today there are plenty of toothpaste choices; lots of colors and tastes to choose from, and some kinds of toothpaste are made just for children. When you're choosing a kind of toothpaste, make sure it has fluoride (氟化物). 5．When you brush your teeth, you don't need a lot of toothpaste: just press out a bit.
| A．They used lemon juice, salt or other things to clean their teeth. |
| B．Tooth brushing became popular during the World War I. |
| C．Fluoride makes your teeth strong and healthy. |
| D．Today they're made of soft plastic and are much easier to use! |
| E．To avoid toothache, they had their teeth pulled out. |
同类型试题
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
