In the formula $$R = 1 - \frac{{6\sum {D^2}}}{{N\left( {{N^2} - 1} \right)}},\,'D'$$     stands for·

A. The central limit theorem B. The law of statistical regularly C. The law of inertia of large numbers D. None of the above

A. Sampling error B. Measurement error C. Coverage error D. Non-response error

A. Both (A) and (R) are true B. (A) is true, but (R) is false C. (A) is false, but (R) is true D. Both (A) and (R) are false

A. 0 B. 1 C. 0.4 D. 0.8