which set of molecules is best represented by letters a and b?

The answer is 1. A: oxygen and water; B: glucose

Explanation:

Organic molecules:

Molecules that contain carbon are called organic molecules. The definition of organic compounds has changed quite a number of times over the years. Previously, it was believed that all compounds obtained only from natural sources or living matter are organic. Later, in 1828, Frederich Wöhler disproved this hypothesis by synthesizing urea - an organic compound - by heating ammonium cyanate (an inorganic  compound).

According to the current definition, all compounds that contain one or more carbon atoms covalently bonded to hydrogen (C-H) and other elements such as , sulfur, phosphorous, oxygen or nitrogen etc, are called organic compounds. The C-H bond defines an organic compound.

In case of the above scenario, glucose (C6H12O6) is the organic compound/molecule because it contains six carbon atoms bonded to hydrogen and oxygen.

All compounds/molecules that do not contain carbon bonded to hydrogen are inorganic. In this question, water and oxygen are inorganic as neither contains carbon bonded to hydrogen.

the major parts of the digestive system:

salivary glands.

pharynx.

esophagus.

stomach.

small intestine.

large intestine.

rectum.

accessory digestive organs: liver, gallbladder, pancreas.