A student draws a graph showing the speed of different galaxies moving away from the Earth plotted against their distance from the Earth. From the best straight line on the graph, what is the value of the Hubble constant $H_0$?
- A$2.0 \times 10^{-18}\ \text{s}^{-1}$
- B$2.2 \times 10^{-18}\ \text{s}^{-1}$
- C$4.5 \times 10^{17}\ \text{s}$
- D$5.0 \times 10^{17}\ \text{s}$