A heat engine takes heat QH from a hot reservoir and uses part of this energy to perform work W. Assuming that QH cannot be changed, how can the efficiency of the engine be improved?
1. Decrease the work W, the heat QC rejected to the cold reservoir remaining unchanged.
2. Increase the work W, the heat QC rejected to the cold reservoir decreasing as a result.
3. Decrease the work W, the heat QC rejected to the cold reservoir decreasing as a result.
4. Increase the work W, the heat QC rejected to the cold reservoir increasing as a result.
5. Increase the work W, the heat QC rejected to the cold reservoir remaining unchanged.