The snack food market has recently seen an explosion in the production

Analysis of argument:
1. Fast rise in production and sales of "100- Calorie packs” which provides exactly 100 calories per portion.
2. 100- Calorie packs costs more and sells for nearly same price as traditionally sized portions which are 2-3 times 100- Calorie packs.
3. First explanation of the rise in sales of "100- Calorie packs”: Consumers unconcerned with impression of the small packs and willing to pay more to avoid having to measure out their portions.
4. Another explanation of the rise in sales of "100- Calorie packs”: At least in the case of snacks for which it has sold well, the 100- calorie pack still looks and feels "substantial" enough to appeal to dieters who lack the self control to limit their consumption of snacks from larger packages.

Pre thinking:
The production of 100- Calorie packs is increasing despite of its high cost of production to the producer while selling at same price as traditional product. So producer must be able to sell large number of these to get more aggregate profit even though profit per unit is less. This becomes irrelevant because we are looking for consumer behavior and not production behavior.
The Sales of 100- Calorie is also on rise despite the fact that it sells for nearly same price as traditionally sized portions which are 2-3 times 100- Calorie packs.
So the consumers are using it increasingly and the only major difference from traditional product s is that the 100- Calorie packs which provides exactly 100 calories per portion.
So the reason for increase must be around the exact 100 calories per portion per portion which it provides.

The first explanation says that consumer is using it more often to avoid measuring out their portions. So the consumer is too busy to measure the portion they eat and can’t eat more than 100 calories.

The second explanation relies on the reason that it is getting popular because of dieters who lack self control and hence chooses 100- calorie pack to limit their consumption.

Answer choice analysis:

A. Consumers are willing to pay exactly the same price for 100-calorie packs sold in vending machine as for traditionally sized snack portions sold in vending machine.
Incorrect: This is not supporting or undermining the argument but repeating the fact given in passage.

B. A large number of buyers of 100-calorie packs consume them as light desserts after large meals that have left them feeling too full for traditionally sized snack food.
Incorrect: Not related to any of the explanations. The explanations rely on either not wanting to measure or on dieters without self control.
C. Although the 100-calorie packs have begun to sell well across a large variety of demographics, busy young professionals were the first group to purchase them frequently.
Incorrect: Supports the first explanation but doesn’t undermine the second one as it doesn’t say anything about dieters.
D. Because the 100-calorie packs require more packaging per ounce of food than the traditionally sized portions do, manufacturers must charge more per ounce to make the same relative profit as on traditionally sized portions.
Incorrect: Explanations are not taking about manufacturers but about the users.

E. Sales of 100-calorie packs have been uniformly poor at stores where they are displayed alongside traditionally sized portions, even for the same snacks whose 100-calorie packs are bestsellers at other stores.
Correct
The sales have been uniformly poor at stores where they are displayed alongside traditionally sized portions shows that a big section people lack self control and will go for larger sized portion if displayed together. The second explanation talks about this behavior and hence is supported by this answer choice.

It also undermines the first explanation which says that consumer is using it more often to avoid measuring out their portions. Had that been the reason the sales of 100-calorie packs wouldn’t have gone down when displayed with traditional packs.