has been shifted is used when some external factors attributed to that shift.....

eg: The cargo has been shifted by the labourers...here he cargo cant shift by itself...so an external factor - labourer is introduced to do the shifting.

has shifted is used when something is shifting by itself. No external factor plays a role in the shifting.

eg: John has shifted his residence from Florida to California.

Coming to our case...if you see in the last part of he sentence - by the rapid motion of the galaxy away from the Earth - this indicates an external factor introduced......So A is the right choice...

Great explanation on this one jangojess!

is the usage 'extent of' wrong?

if extent of is right, then E can be rite?

thoughts?

Ranji, there are lots of times when you can say 'extent of' -- i.e., What is the extent of the damage? -- but this is a separate case where it doesn't work.

E is wrong because it changes the meaning of the sentence. The way E reads the red shift is the shift of light from a distant galaxy towards red...etc, but "from a distant galaxy" is simply being used to described the type of light, not where the light is shifting from. That's a usage change.

I hope that was clear!

makes sense! thanks!

makes sense! thanks!