即使对程序的所有路径都进行了测试，程序也可能存在没能检查出来的缺陷，其原因可能是______。

A．程序可能会因为缺少某些路径而存在问题

B．即使是穷举路径测试也绝不能保证程序符合其设计规格说明

C．穷举路径测试也可能不会暴露数据敏感错误

D．以上全部

What is the basic principle of the magnetic compass（）.

A.Magnetic materials of the same polarity repel each other and those of opposite polarity attract

B.The Earth's magnetic lines of force are parallel to the surface of the Earth

C.Magnetic meridians connect points of equal magnetic variation

D.The compass needle（s）will，when properly compensated，lie parallel to the isogonic lines of the Earth