The surface temperatures and apparent magnitudes of stars in a hypothetical star cluster are measured and plotted in the similar way as that of the HR-diagram. If it is found that most of the stars in the cluster lie on a band which is approximately parallel to the main sequence of the HR-diagram but shifted downwards by 10, what approximately is the distance of this star cluster from the Earth? 1000 pc 400 pc 700 pc 100 pc