B. Geologists determined the depths of layers when the waves were reflected back to the source.
I believe it's 1. Duplication of DNA has already happens.
Short answer - to breathe.
Long answer - the black streaks on the trunk of birch trees are called lenticels, and their function is to enable the exchange of gases between the tree and the air. So, in a way, this makes the whole process of photosynthesis a lot easier for birch trees.
<span>an organism’s living and nonliving interactions with its environment </span>
The place where an organism lives
