Regarding energy, the following statements are correct: (a) Coal, oil, natural gas, water, wind and electricity are all conventional energy sources; And (b) nuclear energy and electricity.

A, coal, oil, natural gas, hydropower are conventional energy, wind energy is a new energy, so A is wrong;

B, nuclear energy, solar energy, tidal energy, geothermal energy, wind energy are all new energy, and water energy is conventional energy, so B is wrong;

C. energy directly from nature without processing and conversion is primary energy.

The energy directly or indirectly converted from one-time energy is secondary energy, so C is wrong;

D, the important way to solve the energy problem is to develop and utilize new energy, especially nuclear energy and solar energy, so D is correct;

So choose D.