Introduction:
Cost benefit analysis (CBA) is a systematic approach to evaluating the costs and benefits of a project, decision, or policy. It helps in determining whether the benefits outweigh the costs, and whether the project or decision is economically justified. In this question, we are asked to identify which of the given options is a cost benefit analysis.

Explanation:
- Effectiveness:
Effectiveness refers to the degree to which a project or decision achieves its intended objectives or goals. While effectiveness is an important factor to consider in decision-making, it is not the same as cost benefit analysis. Effectiveness focuses on the outcome or result of a decision, whereas cost benefit analysis evaluates the economic feasibility of a decision by comparing the costs and benefits.

- Efficiency:
Efficiency refers to the ability to accomplish a task or objective using the least amount of resources, such as time, money, or effort. While efficiency is another important factor to consider in decision-making, it is also not the same as cost benefit analysis. Efficiency focuses on optimizing resource utilization, whereas cost benefit analysis focuses on the economic evaluation of a decision.

- Both (a) and (b):
The correct answer is option 'B', which states that efficiency is a cost benefit analysis. This is because efficiency is an important aspect of cost benefit analysis. When conducting a cost benefit analysis, it is essential to consider the efficiency of resource allocation and utilization in order to accurately assess the costs and benefits of a decision.

- None of these:
This option is incorrect because efficiency is indeed a component of cost benefit analysis.

Conclusion:
Cost benefit analysis is a systematic approach to evaluating the costs and benefits of a project or decision. While effectiveness and efficiency are important factors to consider in decision-making, they are not the same as cost benefit analysis. The correct answer to the question is option 'B', as efficiency is a component of cost benefit analysis.