1. Which of the following gases is need by plants?

Carbon dioxide

Explanation:

To perform photosynthesis, plants need three things: carbon dioxide, water, and sunlight. for photosynthesis. Carbon dioxide enters through tiny holes in a plant's leaves, flowers, branches, stems, and roots. Plants also require water to make their food.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

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