A metal sphere with radius $r$ is released into a tank of water. While it descends with speed $v$, it is acted on by a drag force $F$ defined by $F = krv$, where $k$ is a constant. What are the SI base units of $k$?
- A$\text{kg m}^{-2}\text{ s}^{-1}$
- B$\text{kg m}^{-2}\text{ s}^{-2}$
- C$\text{kg m}^{-1}\text{ s}^{-1}$
- D$\text{kg m s}^{-2}$