Preteins vary widely in structure, whereas nucleic acids have rather uniform structures. how do you account for this major difference?

As proteins vary widely in structures than that of nucleic acid there will be greater structural  and functional diversity of proteins  than nucleic acid.

Explanation:

Proteins are the macromolecules which have more structural diversity than any other macromolecules such as carbohydrate,lipid,nucleic acid.

  The are 4 types of protein structure primary structure,secondary structure,tertiary structure and Quaternary structure.Due the existence of many types of structure various protein exhibit various functions.

 On the other hand nucleic acid such as DNA has widely accepted secondary structure discovered by watson and crick.As a result there is no such structural diversity exist in nucleic acid.

the best answer is d because the strong cohesion is caused by the ability of water molecules to undergo hydrogen bonding.

a is incorrect because when water solidifies, it becomes   ice, which expands and occupies a bigger volume for the same mass of water in its liquid state.

b is incorrect because water has high surface tension. besides bonding to itself it hydrogen bonds to other molecules at the top decreasing possibility for breaking of attractive forces.

c is incorrect because the water molecule has oxygen which is highly electronegative and so pulls the electron pair towards itself creating a dipole moment, making the molecule polar.

e is incorrect because water has strong adhesion, ability to stick to other molecules such as glass because of this molecules having stronger hydrogen bonding than water.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.