Which of the following completions for the sentence results in a simple sentence structure?

The choice that results in a simple sentence structure is the one that has a single independent clause, which expresses a complete thought and does not contain any dependent clauses or additional clauses that would complicate the sentence structure.

In this case, the selected option conveys a clear, concise idea: "lost many customers due to the opening of a competing vendor on another street." This is an independent clause that stands alone as a complete thought, making it a simple sentence.

The other options involve additional clauses or phrases that make them compound or complex sentences. For instance, the first option includes a cause-and-effect clause that adds complexity, the third mentions a clause that begins with "as," indicating a cause related to the subject, and the fourth example contains a contrasting idea introduced by "but." These elements lead to more complex sentence structures, diverging from the criteria of a simple sentence.