Asexual reproduction occurs when two or more offspring are produced without requiring another parent. All of the individuals will be identical to the parent (reducing genetic diversity), as they have genes that are copies of the parent's genes. Therefore, B and D are incorrect.
Asexual reproduction requires less energy than sexual reproduction, but still some energy will always be necessarily used. Therefore, A is incorrect.
In asexual reproduction, only one parent is needed, there is no need for another parent to participate. Therefore, the correct answer is C. reproduction without another parent.