How do astronomers know that dark matter exists? A. Because it emits electromagnetic radiation
B. Because it can be directly observed
C. Because its gravity affects the motion of objects around it
D. None of the above

C. Because it's gravity affects the motion of objects around it.

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.