In a single molecule of water, the two hydrogen atoms are bonded to a single oxygen atom by?
a. hydrogen bonds.
c. polar covalent bonds.
e. van der waals interactions

c.Polar covalent bond

Explanation:

Hydrogen bonds: It is that bonds which is formed between H-atom  and high electronegative  elements such as O, F etc.

Polar covalent bonds: It is also covalent bond .Covalent bond is formed by sharing of electrons between two atoms.But in polar covalent bond the sharing of a pair of electrons between two atoms is unequal.Because one atom spend more time with electrons than the other.

Van der Waals interaction:It is also type of force.It  includes repulsion and  attraction between atoms. molecules and surfaces, as well as other intermolecular forces.It is different from covalent or ionic bond.They are caused by the correlation fluctuating polarization of nearby particles.Three types of van der waal force are disperson force ,Dipole-Dipole  and hydrogen bond.

In a single molecule of water , the two hydrogen atoms are bonded to a single oxygen atom by polar covalent  bond.Because oxygen is slightly negative and hydrogen are slightly positive in a water molecule and oxygen more attract  electron towards itself.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.