A good estimator should have the following properties:
- **Consistency**: The estimator converges to the true value as the sample size increases.
- **Sufficiency**: The estimator makes use of all available data without discarding useful information.
- **Efficiency**: The estimator has the smallest variance among all unbiased estimators.
Step 2: Analyzing the options.
(A) Consistent: Correct. Consistency ensures that the estimator converges to the true parameter value as the sample size increases.
(B) Sufficient: Correct. A sufficient estimator uses all available information and does not lose relevant data.
(C) Efficient: Correct. Efficiency refers to the estimator having the least variance among unbiased estimators.
(D) All of the above: Correct. A good estimator should possess consistency, sufficiency, and efficiency.
Step 3: Conclusion.
The correct answer is (D) All of the above, as all these properties define a good estimator.
Final Answer:} All of the above.