+1 for D.

A decade after the demise of early entrants such as Webvan, each of the successful competitors in the online home-delivery industry have either developed new world-class supply-chain capabilities or already have existing strengths in logistics for traditional "bricks and mortar" stores.

(A)have either developed new world-class supply-chain capabilities or already have
(B)either have developed new world-class supply-chain capabilities or already have
(C)has developed either new world-class supply-chain capabilities or already
(D)either has developed new world-class supply-chain capabilities or already has
(E)has either developed new world-class supply-chain capabilities or has already

Ta

>>
A,B - Clearly Subject Verb Disagreement.

C - Either X or Y should have X and Y parallel. Are "existing strengths in logistics for traditional "bricks and mortar" stores. " developed? No, they are already existing. So, positioning "either" after "has developed" changes the original meaning of the sentence, even though it is grammatically correct.

D - Again X and Y in "Either X or Y" have to be parallel.
"has developed new world-class supply-chain capabilities" - X (verb + noun)
"already has existing strengths ..." - Y (adverb + verb + noun)


E - "developed something" and "has already existing..." are parallel and have "verb + noun" format.

IMO E.

+1 for D
Use of have is wrong - A and B are out
C is wrong because of wrong construction.
E is wrong because of usage of has haseither ..... or has[/u]

+1 for D

A decade after the demise of early entrants such as Webvan, each of the successful competitors in the online home-delivery industry have either developed new world-class supply-chain capabilities or already have existing strengths in logistics for traditional "bricks and mortar" stores.

(A)have either developed new world-class supply-chain capabilities or already have
(B)either have developed new world-class supply-chain capabilities or already have
(C)has developed either new world-class supply-chain capabilities or already
(D)either has developed new world-class supply-chain capabilities or already has
(E)has either developed new world-class supply-chain capabilities or has already

Friends its this way.....

Give predominance for Each if it comes first....else if it comes after some subject then give for Subject....

In the above sentence.....the word each has to be given more stress....So has should be used rather than have....Knock out options A and B
Check for parallelism now...

No need to tell which one is parallel...its none other than D