How did farmers observed by Charles Darwin take advantage of natural variation to improve their livestock?

They used artificial selection

Explanation:

Breeding animals who had desirable or good traits. For example, they bred cows who produced the most milk and plants that produced the most vegetables. :))

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.

did you fail the test? xd