The greatest challenge that Amazon faces from Walmart and Kroger, which offer curbside pickup of online groceries, is C. figuring out where to set up curbside pickups at Amazon distribution centers.
With Amazon's giant online presence and performance, it can dominate the online grocery market. However, it has Walmart and Kroger to contend with because these have developed curbside pickups for online grocery orders.
The above statement implies that Amazon does not have a problem figuring out the best delivery means, the local grocery stores to buy products from, or the locations to build Amazon grocery stores.
Thus, the challenge that Amazon faces from Walmart and Kroger is Option C.
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