这题不理解，请解释说明

问题如下：

For which type of ESG activity would it be easiest to evaluate the impact on a portfolio’s performance?

选项：

A.Excluding an industrial sector (e.g., tobacco)

B.Implementing a program of active engagement

C.Screening of companies for exploitive labor practices in their supply chain

解释：

A is correct. It is relatively easy to assess the performance drag or enhancement that comes from excluding an industrial sector. There may even be benchmarks available reflecting the same restrictions. It is more difficult to demonstrate the value added by a program of engagement. It would be difficult to monitor the labor practices in the supply chains of all companies in a benchmark.