无指向性点源几何发散衰减的基本公式为（）。
A．A
B．B
C．C
D．D
参考答案：A
29. _____ the lack of workforce in many industries, workers are now commanding higher salaries than they used to be.
A．Regardless of
B．Due to
C．In case of
D．According to
试述辽朝政治制度的特点。
