Which of the following is an example of a contact force?

By the fall of an apple from a tree.

Explanation:

The first law of Newton’s is the law of movement that address inertia and how gravitational forces works. The storie about how Newton found this law is in a biography “Memoirs of Sir Isaac Newton’s Life”(1752), written by William Stukeley, which mentions the apple anecdote: “After dinner, the weather being warm, we went into the garden, & drank thea under the shade of some apple trees… he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind…. occasion’d by the fall of an apple, as he sat in a contemplative mood.”