What 20th century discovery changed the view of geologists toward plate tectonics?
Answer
A) discovery of old layers on the continents that indicated plates were moving
B) discovery of the young age and active nature of the ocean floor
C) discovery of the Ring of Fire and the San Andreas Fault

You wrote two different questions that somewhat affect the answer. Which is it? And why are you thinking that people here are now going to do all your homework?