Concept:
When the broad outlines of the major continents are examined, a recurring geometric pattern is observed in their shapes.
Step 1:
Most continents are broad in the north and taper to a point towards the south, giving them a roughly triangular outline. Examples include South America, Africa and the Indian peninsula, all of which narrow southward.
Step 2:
Because this tapering, wedge-like form is repeated across the continents, the most common shape attributed to continents is the triangle.
Answer: Option (1) — Triangle.