Approximately two hundred brands of personal computers are being manuf

Only B and D can catch your attention.

However, only one can be right and it is B. D is incorrect because it talks about profit. However the argument is not concerned about profits. It is only focused on including brands to increase sales. Thus, B deliberately weakens the argument by giving a reason that even if more brands are included, sales won't increase.

Thus, B is the best.

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Understand :
- we limit our inventory ( available stock with the company at present) to 8 most popular brands
- We will expand our inventory to include "ten best selling brands"
- why?? INCREASE GREATLY the number of computers we sell

- Flaw

Think:
Typical GMAT pattern - OVERLAP of groups.... I want to increase the sale of computers from my store. I already have 8 most popular computers , and now i am going to expand my inventory to 10 best selling brands. why?? I want to increase my sale SUBSTANTIALLY. But what if i get to know that the most popular are themselves best selling?? that is most of my current most popular brands are actually the best selling then including the same brands once again MAY NOT increase my sale GREATLY
.Have I made sure that both are actually different?? that is there is a minimal overlap of both groups??

- In this answer choice we are only considering the most popular brands and comapring capabilities among them. HOW does this choice help us ecaluate the efficacy of my plan to increase sale by include BST selling brands??
.
- If 7 of most popular brands are also the most selling (best selling) then including 2 top selling brands may not increase my sale GREATLY. Sure it may increase but not greatly

-This does not talk about a weakness in my plan. also there is a reason why "best selling brands" is used. It means consumers actuallu but those specific brands in great numbers.

- "profit" is not our concern. we are concerned with SALE

-"The " that means one particular brand is loosing its market to someone else. But are we including that brand in our inventory?? WE DONT KNOW

They are currently selling 8 most popular brands and expect that by selling 10 best selling brands their sales figures will shoot up.
We need a weakener.
Option B says that almost all the sales are accounted for by the 7 most popular brands hence inclusion of 2 more brands may not really have a big impact.
Hence B is the answer

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The plan here is to increase the number of computers in the inventory greatly by including 2 more brands. Choice B would be the most weakening sentence because if top 7 brands account for almost all the computers sold then it would make minimal change in the number of computers in the inventory if he includes two more brands. Hence, B is the answer.

I think here one of the major factor is that the question talks about best selling brands and not cheap/popular brand. A cheap brand can be best-selling. For example Oppo is a cheap brand in India but it is highly possible that it is one of the best selling brand