Answer:
The periosteum is one source of precursor cells which develop into chondroblasts and osteoblasts that are essential to the healing of bone. Other sources of precursor cells are the bone marrow (when present), endosteum, small blood vessels, and fibroblasts.
Answer:
A red "L" is a symbol for low air pressure.
Answer:
Mice have four legs, four feet and one tail per unit-mouse.
Answer:
rise over run
Explanation:
rise refers to the number of units going u or down a graph
run refers to the number of units going left or right
it is seen as so;
,
, or 
Don't panic when I included "delta". Delta, it refers/means the small mathematical triangle found beside the rise and run symbols of y and x