The types of power that are relatively non-polluting from the given options are:
I. Wind - Non-polluting during operation, but there are some environmental concerns related to manufacturing and land use. II. Solar - Also non-polluting during operation, though there are concerns related to the manufacturing process and waste management of solar panels. III. Hydroelectric - Generally low emissions during operation, but can have significant ecological impacts on waterways and habitats. IV. Nuclear - Produces very low greenhouse gas emissions during operation, but concerns exist regarding radioactive waste and the potential for nuclear accidents.
Given this analysis, the best answer that identifies relatively non-polluting energy sources is:
I, II, and IV
However, it's important to note that while hydroelectric power may have ecological impacts, it is often considered low-emission, and nuclear energy is also low in greenhouse gases but has other significant concerns. Therefore, some might include hydroelectric in a broader interpretation of "non-polluting." Thus, the safest interpretation based strictly on the provided options is:
I, II, and IV.