Question #$15$: Dr$.$ Jones, the history professor, administers a $30-$item test the first day of class to ascertain his students initial level of knowledge of American history. Bob got a $0,$ Joe a $10,$ Betty a $20,$ and Mark and Sheela each got a perfect $30.$

$($a$)$ In all likelihood, what scale of measurement is this? Explain

$($b$)$ Can Dr$.$ Jones conclude that Bob doesn't know anything about American history? Explain

$($c$)$ Is Betty's knowledge of American history twice as great as Joe's? Explain.

$($d$)$ Can Dr$.$ Jones conclude that Mark and Sheela have an equally good knowledge of American history? Explain.