请大神指教这篇英语阅读理解答案是什么?

请大神指教这篇英语阅读理解答案是什么?
Most of the world’s diamonds come from Africa,but there is one place in the United States where they are founds.It is near Murfreesboro,Arkansas.
Diamonds were first found near Murfreesboro in 1906.About 50 thousands have come from this field.One 40 carat (克拉) diamond was the largest ever found in North America.But most of the stones were too small to make mining worthwhile.Soon all mining stopped there.Today a visitor to Murfreesboro hunt for diamond himself.
A few diamonds have been found in sand and gravel(砾石) along the Great Lake,too.This is not where they were originally found.They may have been formed far to the north and carried south by the last great glaciers (冰川).
46.Most diamonds have been found in ____.
A.North America B.South America C.Africa D.Arkansas
47.Diamonds in their original ground have been found _____.
A.in Arkansas B.in several states C.around the Great Lake D.All of the above
48.The Murfreesboro field was ____.
A.never mined B.mined until there were no more diamonds
C.not worth mining D.mined large valuable stones
49.In Murfreesboro today,the visitors can____.
A.watch miners at work B.explore an old mine C.hunt for diamonds D.find large valuable stone
50.The diamonds found along the Great Lakes were____.
A.carried there from other places B.not found in their original ground
C.found in the rocks where they were formed D.both A and B