An experiment or survey must be controlled in order to receive accurate results.
In an experimental group, the independent variable is changed. But in the control group, the independent variable stays the same.
Answer:
C, D.
Explanation:
C: The flowing lava creates extra rock. For example, entire islands are formed via this process of volcanos erupting, lava cooling, repeat.
D: Silt from erosion (erosion itself is considered destructive, but the resulting silt can turn into something constructive.) can build up entire mounds or mountains over time.
