Which statement best describes an environmental consequence of unsealed landfills? Landfills can produce carbon dioxide that leak into the atmosphere. Long-term exposure to mercury and lead in landfills can cause cancers.
Heavy metals are released as leach ate into surrounding waterways.
Materials in landfills undergo decomposition for hundreds of years.

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.

the supermassive black hole is in the middle of the galaxy.