Read the following paragraph from the Introduction (paragraphs 1-4].
Volcanoes are openings where lava,
small rocks and steam erupt onto
the Earth's surface. The volcano that
erupted most recently is a shield
volcano. This means it is built out of
lava, or melted rock. Lava comes up
from beneath the Earth and out of a volcano. Then it flows on the
surface.
What does the author mean by "surface"?

A. The top layer
B. The area below
C. The middle part
D. The part deep within