Dr. Oz goes undercover as a New York City cab driver to give passengers a pop-quiz on stress and a big surprise.

Click here to watch Part 2 and see the contestants face off in the studio.

After years of trying to get pregnant, doctors told Kelsi Pierce it would be near impossible for her to conceive a child. However, Kelsi got the surprise of her life when her mom volunteered to be her surrogate — and she found out she, too, was pregnant!