25. Productivity can be increased by a. Raising minimum wage
b. Underutilizing resources
c. Improving the human capital of workers
d. Restricting trade with foreign countries

C

Explanation:

improving the human capital of workers means improving their skills on the job with special training or something similar to that, therefore creating trust between the worker and the job, when this happens the worker gains the knowledge to do his/her job properly and doesn't feel the need to not want to work because now they know how to do it, and if they do it properly then that's it better for the company in the long run.