In order of decreasing light-transmitting capabilities of materials, which is correct sequence?

==>  A piece-o-cake for light to get through.
==>  Quite easy for light to get through.
==>  Not very easy for light to get through.
==>  Somewhat difficult for light to get through.
==>  Pretty tough for light to get through.
==>  Virtually impossible for light to get through.
==>  Totally impossible for light to get through.

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Answerthe distance between the two ends of the galaxy is 150,000 light years;