Look at the 4th decimal place to decide whether to round up or down.<br><br>&bull; 12.2378: the first three decimal places are 2-3-7.<br>&bull; The 4th decimal digit is 8, which is &ge; 5, so we round up.<br>&bull; 12.237 rounds up to 12.238<br><br>Final Answer: C: 12.238