The portion of the spinal column is joined to the iliac bones of the pelvis.

The sacrum portion of the spinal column.

Explanation:

the sacrum is located at the base of the lumbar vertebrae, which is part of the spinal column, and connects it with the iliac bones. The sacrum helps in the strengthening and stability of the pelvis.

the answer is; comparing the frequency of collisions with and without the device

this makes the anti-collision system an independent variable and the collisions a dependent variable. if there are fewer collisions with an anti-collision system that without, then it can be stated that the system is a success. essentially, collisions under an anti-collision system are compared with the frequency of collisions by cars with the human drivers.