The lumen of a human aorta is $2\ \text{cm}$ wide. A human red blood cell has a diameter of $7\ \mu\text{m}$. If red blood cells were placed in a line end to end, how many would span the diameter of the aorta lumen?
- A$2.9 \times 10^{-3}$
- B$2.9 \times 10^{-2}$
- C$2.9 \times 10^{2}$
- D$2.9 \times 10^{3}$