Which bone forms the back and base of the cranium?

The occipital bone is the correct choice because it specifically forms the back and base of the skull, which is crucial for providing structural support for the head and protecting the brain. This bone contains the foramen magnum, the large opening through which the spinal cord connects to the brain, highlighting its importance in anatomical positioning and function. The occipital bone also interacts with several other bones in the skull, playing a vital role in the overall anatomy of the cranium.

In contrast, the parietal bones are primarily located on the sides and roof of the skull, while the frontal bone forms the forehead and the anterior part of the skull. The temporal bones are situated beneath the parietal bones and in front of the occipital bone, contributing to the sides of the skull and the structures of the ear. Each of these bones has specific roles within the cranial structure, but only the occipital bone is responsible for the back and base, making it the right answer for this question.