Question

what first caused people to consider that the continents were once one large landmass?
glacier evidence in warmer countries
continents looked like they fit together
studying the valleys of the ocean floor
similar fossils were found on many continents

Explanation:

To determine what first caused people to consider continental drift (continents once being one landmass), we analyze each option:

• "glacier evidence in warmer countries": This relates to climate and glaciation but isn't the primary initial clue for continental drift.
• "continents looked like they fit together": The visual appearance of continents (like Africa and South America) seeming to fit like a puzzle was one of the earliest and most intuitive pieces of evidence that led people to think they were once connected.
• "studying the valleys of the ocean floor": Ocean floor studies (like mid - ocean ridges) came later in the development of plate tectonics, not the initial clue for continental drift.
• "similar fossils were found on many continents": While this is strong evidence, the visual fit of the continents was a more immediate and early - noticed clue that made people start considering the idea of a single landmass.

Answer:

B. continents looked like they fit together