Which of the Following Is an Example of Signaling

Which of the following is an example of signaling?

A) Pat is considering the purchase of a used car. Before making the purchase he has the car checked by an auto mechanic.
B) Zach is applying for a new life insurance policy. Before writing the policy, the insurance company requires Zach to be examined by a doctor.
C) Denise is applying for a new joc. Before hiring her, the firm requires Denise to take a drug test.
D) Marcus is planning to ask for Chaquila's hand in marriage. Before asking her, he buys her a box of her favorite chocolates and takes her to dinner at her favorite restaurant.