（）is an energy form found in nature that has not been subjected to any human engineered conversion process.It is energy contained in raw fuels， and other forms of energy received as input to a system.

（）is an energy form found in nature that has not been subjected to any human engineered conversion process.It is energy contained in raw fuels， and other forms of energy received as input to a system.
A.Preliminary energy
B.Principal energy
C.Premium energy
D.Primary energy
正确答案：Primary energy