What is Wrong with this Dialogue?

Professor:  "What was invented in the late 1400's?"
Student 1: "The light bulb!"
Student 2: "Trains?"
Student 3: "Car."
Me: "...................."

(once again, this sh*t really happened)

The correct answer is: The Printing Press.
1. Light bulb = 1900's
2. Trains = 1800's
3. Car = 1900's

*head-desk*