Title: Geological history of Earth.
Question: What type of rock was the Cretaceous notable for forming the most amount of?

Title: London.
Question: What failed plan to install a major network of roadways within the City of London were eventually scrapped in the 1970s?

Title: Samurai.
Question: Who was the first warrior to become imperial advisor?

Title: Light-emitting diode.
Question:
Which LEDs are considered dangerous by a 2011 study?