What is thought to have caused the ice ages?

A. Earths magnetic field
B. Earths precession
C. Earths rotation
D. Earths tilt

b) chemical ( the chemical breakdown of food is accomplished by enzymes. )

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if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.