Zarrolou wrote:
"unlike traditional retailers" who? the subject must follow the comma, out C and A.
Then we can eliminate B because the form COMMA + ING modifies the preceding clause, and in this contest is wrong. This kind of modifier expresses the consequences of the previous verb ( for example), as you see this is not the case.
We are down to D and E. In E "have been able" must be parallel with the next verb, but this option uses "stayed": not parallel.
D "have been able
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