A large number of weak that are inconsequential by themselves can amount to an important, large, attractive force between the two surfaces of large interacting biomolecules, such as a small protein and the larger protein bound to it.

Weak van der waals forces

Explanation:

Van der waals forces are  non-covalent bonds electrically induced between two atoms or molecules.

By themselves, van der walls forces are inconsequential. A large number together play crucial roles.

They play a crucial role in determining the structure, stability and function of systems.

In proteins, it contributes in its interaction with other molecules.

it is very expensive

explanation:

the answer is b.) hydrogen bonds between bases.