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从一个关系数据库中选出指定的若干属性的操作称为________
II型呼吸衰竭的血气分析结果应是APaO2<60mmHg,PaC02正常BPaO2正常,PaC02≥50mmHgCPaO2<60mmHg,PaC02>50mmHgDPa O2≤60mmHg,PaC02≥50mmHgEPa O2≥50mmHg,PaC02≥50mmHg
2. About a quarter of American adults say that they __________ a book in whole in the past year.
Many Americans understand the life-saving value of the seat belt—the national use rate of it is at 90.1%.
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