<p dir="ltr" style="text-align: justify;"><span><span style="">The blank connects two clauses, so it could be filled with a coordinating conjunction or a subordinating conjunction. In other words, all the four choices are possible answers since Choice (A) </span><span style="">if</span><span style=""> can serve as a subordinating conjunction that starts a noun or adverb clause, while Choice (B) </span><span style="">or</span><span style="">, Choice (C) </span><span style="">but</span><span style="">, and Choice (D) </span><span style="">and</span><span style=""> are coordinating conjunctions that can connect two independent clauses. </span></span></p><p><span><span style="">The key to identifying the correct answer is the meaning of the context. The first clause describes something negative for the customer who requires a model, while the second clause says something positive for this customer. The conjunction that can show a contrast between two situations or even contrast two opposite situations is Choice (C) </span><span style="">but</span><span style="">. </span></span></p>