Narwhals can be called whales of ice: in icy channels, pouds and ice-shielded bays they seek sanctuary from killer whales, their chief predator, and their annual migrations following the seasnal rhythm of advancing and retreating ice.
A. their annual migrations following
B. their annual migrations which follow
C. their annual migrations follow
D. whose annual migrations following
E. whose annual migrations follow

This has something to do with the structure of a sentence. Generally compound sentences involving the coordinator 'and' will have to balance the structure on either sides of the said conjunction parallelly. You may find that in the clauses follows the semicolon, the first part is a full-fledged while you expect the same such clause in the second part after ‘and’ having a full verb. . Unfortunately choices A, B, D and E contain simple phrases involving participles or sub clauses having which or whose. Only C sticks to the basic grammar of structure.
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@skamal

Pl follow this example.

1. X ate water melon, his children looking at him —This is a simple sentence where x is the subject, and ate is the verb and the fruit, the object; What follows after the comma is a simple phrase, without a verb( looking’ is a present participle , not a verb) . We cannot use an ‘and’ in this case after the watermelon because and we can join only two equal things, be it two clauses or phrases or simply words. The word ‘and’ prevents the modifier phrase from being grammatically attached to the IC.
2. X ate watermelon as his children looked at him --- This is complex sentence, involving an independent clause (IC) and a dependent clause, both of which have their own verbs and hence they are called clauses. The word ‘as’ is a subordinate conjunction and now after having used a subordinate conjunction, we cannot use again another co-ordinate conjunction such as ‘and’.
3. When you follow an IC with and, then what must follow must also be an IC. Since ‘and’ is not underlined and since that will be part of any answer, then the only choice that will go with that structure is a clause that has a verb in the second arm ; only C has that structure.

I hope it is clear now why A violates sentence structure
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Alicia Helle, an online student at the UW, "Obtaining my degree online has been a blessing. With two small children, I am able to work when it is convenient for my family and me. I have nothing but positive comments and experiences from my time at UW-Stout.”

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Narwhals can be called whales of ice: in icy channels, pouds and ice-shielded bays they seek sanctuary from killer whales, their chief predator, and their annual migrations following the seasnal rhythm of advancing and retreating ice.
A. their annual migrations following
B. their annual migrations which follow
C. their annual migrations follow
D. whose annual migrations following
E. whose annual migrations follow

Can anyone explain option a & c in detail

if we were to go by it technically ... the they seek will have to be in parellel with they follow and not following

After three minutes and a half I got it right. The important thing is to hnderstand that the underlined part stillmodifies the narwhales , not their predator.