The correct option is C Research
4R encompasses the strategies and efforts to reduce, reuse, recharge or regenerate, and research.
Reduce stands for minimising the use and wastage of resources. Reuse means the sustainable usage of resources multiple times in different ways. Resources could also be recharged or regenerated if we make a conscious effort to allow the resource to grow back. Research means exploring sustainable alternatives and practices to conserve resources. It is imperative for our sustenance.