<p><span style="font-size: 13.008px;">The correct preposition to use in this sentence is (B )"by".</span><br></p>
<p>The phrase "by the end of the year" indicates a specific point in time, which is when the company had hired more than 100 engineers. The preposition "by" is commonly used to indicate a deadline or a specific time by which something is expected to be completed or achieved.</p>
<p>Example: "I need to finish this report by tomorrow."</p>
<p>In this sentence, "by" indicates that the report needs to be finished before tomorrow arrives.</p>
<p>Therefore, the correct sentence is: "By the end of the year, the company had hired more than 100 engineers to develop its latest wireless technological device."</p>