Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: Which of the following is a crucial piece of evidence supporting scientists' theory of how the continents and the ocean basins formed?
Currents redistribute heat in an unevenly heated liquid.
The presence of mid-ocean ridges and seafloor spreading.