The fourth level of cell organization is the
tissue level
system level
organ level
organism level

The fourth level of cell organization is the organ system.  

the cost of mining is extremely low compared to the money earned from mining, creating income to improve the environment.

all these collisions do one thing, and that thing is explained in the last option. when dusst, rocks and ice collide, they harden and form giant layers of rocks or hard ice.

d)   to harden materials to form different parts of earth’s layers

hope it ,

bioteacher101