17. When rocks are ground and worn away by rocks and sand, it is called_____.
A. abrasion
C. sand blasting
B. filing
D. weathering

18. A rock formation that soil comes from is called______.
A. bedrock
C. parent rock
B. parent soil
D. silt

19. What do you call the breakdown of rook into smaller pieces by physical means?
A oxidation
B. acid precipitation
C. chemical weathering
D. mechanical weathering​