The conclusion of the argument would be - future advances in telecommunications technology will yield products useful almost exclusively to those certain businesses.

We need to keep two things in mind. First, ask the question 'Is the given answer choice necessary for the argument?" If the answer is yes, we make it a contender. Second, apply the negation test on the contenders.

A is out - not necessary for the argument. There is no link between standard technology and the conclusion.
B - I would say is out, because the first line of the stimulus states that the advancements in technology are brought about by the interest of consumers. This could be all the consumers or a specific set of consumers. The tricky part in the question is that it moves from advancement in technology in general to the specific telecommunications industry in line 2 of the stimulus. The choice mixes the two (technology development aspect of line 1 with specific set of customers who want the advancement). While the telecommunications industry could have a few customers interested in the advancement may be all customers express an interest in development of technology in non-telecommunications sectors.
Still let us keep this choice as a contender since a few answers think this is the right choice.
C - The argument has to assume this or else we can not reach the conclusion that it will yield products useful exclusively for a small group of specific businesses. So we keep this as a contender.
D - Out of scope, not necessary for the argument.
E - Irrelevant.

Thus we are left with B and C. Apply the negation test (Negation should weaken the argument):
B - Negation of B: replace a particular group of consumers with any group - Advancements in technology are mainly brought about by desire from any group of customers. Does this weaken the argument - No. According to the first line, "Advancement in technology occurs primarily in areas in which customers have expressed an interest" this could be a particular group or any group or all the consumers. Hence we eliminate B
C - Negation of C: Remove not - Improved telecommunications technology will be generally applicable to the needs of all customers. Does this weaken the conclusion? Yes, if it is generally applicable to needs of all the consumers, it undermines the conclusion that it will be beneficial to an exclusive set of customers (businesses).

Hence pick C

Hope this helps.