The first vertebrates appeared in which period?
a. cambrian
b. ordovician
c. silurian
d. devonian

Molecular models of two different substances are shown below. in the molecule on the left, the oxygen atom pulls on electrons more strongly than the hydrogen atoms. in the molecule on the right, the two oxygen atoms pull on the shared electrons with the same strength. water molecule, h,o oxygen molecule, oz when the two substances are put in the same container, they do not attract each other. why does this happen? a. they both contain oxygen. b. one is polar and one is nonpolar. c . they are both polar. d. they contain different elements.

The science for classifying and naming organisms is known as

Guard cells control which event? the growth of plants capture of solar energy gas exchange in leaves water absorption in roots