Nina gets a new baby turtle from a friend, and is told to feed it worms. For the first few months, the turtle seemed to grow well. But as time passed, the turtle's shell appeared soft and fragile. Someone suggested that the turtle might not be getting enough calcium in its diet. If this is true for this turtle, dietary calcium is:. A. A limiting factor
B. An environmental condition
C. A habitat condition
D. A natural environmental stressor