everyone / pick up / one piece of trash / a day / about 6.6 billion pieces less

A. If everyone picked up one piece of trash a day, there would be about 6.6 billion pieces less.

B. When everyone will pick up one piece of trash a day, about 6.6 billion pieces would be less.

C. Because everyone picks up one piece of trash a day, about 6.6 billion pieces is less.

D. Unless everyone picked up one piece of trash a day, there will be about 6.6 billion pieces less.