Liquid Paper （修正液） was invented by Bette Nesmith Graham．She was 17when she got a job at a Texas bank as a secretary，even though she didn't know how to type．The company she worked for sent her to a secretary school，and she was typing in no time at all．

The 1950s had seen the widespread use of the electric typewriter，which typed faster but also meant more mistakes．Also，mistakes made by early electric typewriters were very hard to erase，which caused problems for Bette．

In order to make extra money she used her talent to paint holiday windows at the bank．Then one day，it suddenly occurred to her that she could create a paint to cover up type-

writing mistakes．

It worked!In 1956，Bette sold her first bottles of the new product，which she called"Mistake Out"．She made it in her kitchen，and her son Michael and his friends bottled it in the family garage．

By 1957，she was selling 100bottles a month and had gotten a patent （专利） for her product，which she now called"Liquid Paper．"Sales continued to grow，as more and more people heard about Liquid Paper，through word-of-mouth and by reading about it in magazines．

In the 1960s，Bette bought a machine to help her produce Liquid Paper in large quantities．In 1971，she sold 2million bottles．In 1979，she sold the company for 47.5million dollars．She didn't live to see the end of the contract （合同），dying in 1980，at the age of 56，in Texas．

Bette's invention continues to be used every day by secretaries and other people in the office and wherever typewriters are used．

21．When Bette began to work in a bank，she___．

A．was too young to type

B．had graduated from secretary school

C．wasn't experienced in typing

D．taught herself about typing

22．It can be inferred that the first Liquid Paper___．

A．was produced by hand

B．was made by machine

C．was bottled in the kitchen

D．was tested i