字节输入流的父类是（ ），字节输出流的父类是（ ）。字符输入流的父类是（ ），字符输出流的父类是（ ）。
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Questions 19 to 21 are based on the passage you have just heard.According to the passage, how long have dogs been of assistance to humans?
A. For 100 years.
B. For hundreds of years.
C. For less than 100 years.
D. For 1,000 years.
Where can you find proof that dogs have been helping humans for many years?
A. Wood carvings.
B. Scrolls.
C. Wall paintings.
D. All of the above.
Which of the following statements is NOT mentioned in the passage?
A. Specially trained working dogs can sniff for drugs, weaponsand bombs.
B. Dogs are trained to do search and rescue.
C. Dogs are trained to take care of babies at home.
D. Rescue dogs can look for possible survivors during crises.
下列项目中，构成一般纳税人存货采购成本的有
A. 购买商品时支付的保险费
B. 运输途中的合理损耗
C. 入库前的挑选整理费
D. 购入存货支付的增值税
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