Why is it important to have exact standards of measurement ?

Which statement about the stamps is correct?

This drawing shows a human body system. what is the primary function of this body system?

13. a covalent bond between two atoms is likely to be polar if: a. one of the atoms is much more electronegative than the other. b. the two atoms are equally electronegative. c. the two atoms are of the same element. d. the bond is part of a tetrahedrally shaped molecule. e. one atom is an anion.