The partial pressure of oxygen in arterial blood is approximately
A) 40 mm Hg.
B) 45 mm Hg.
C) 50 mm Hg.
D) 70 mm Hg.
E) 100 mm Hg.
Question 2
What structure changes the shape of the lens for far and near vision?
A) aqueous humor
B) ciliary body
C) iris
D) extrinsic eye muscles
E) macula