Interesting. As you start reading the question, you think in your head, it could be "has shifted" too...but then you reach the last bit of the question that says "by the galaxy...". As you reflect on "has shifted" and "has been shifted", you realise they mean different things. "Has been" means it has BEEN ___(shifted, pushed, whatever verb), BY someone else.

(For.e.g. it would be wrong to say "the child has taken home by her mother" when we want to say "the child has been taken home by her mother"

Because this light has been shifted BY the galaxy, we do need "been", and, therefore, 'B' is incorrect.

Experts' help is needed here.

Can any expert please have a look at this problem.

Wondering if there was a reason why you were not convinced by mindful's reply above.

Perhaps because I didn't use the technical terms, grammatical rules, and spoke only on the basis of usage. I guess the vw was hoping to learn about that. Hopefully experts will be able to guide.

vishalwin wrote: Why B is wrong?

Mindful has nailed the error.

B: light from a distant galaxy has shifted toward the red, or long-wave, end of the light spectrum by the rapid motion

light from a distant galaxy has shifted
This wording implies that light from a distant galaxy has shifted ON ITS OWN.

shifted...by the rapid motion
This wording implies that RAPID MOTION caused light from a distant galaxy to shift.

Since the two meanings contradict each other, eliminate B.