Which of the following represents normal breathing characteristics?

The choice indicating a consistent rate of 12-20 breaths per minute accurately reflects normal breathing characteristics in adults. This respiratory rate is considered within the typical range for a healthy individual at rest. In this range, breathing is regular and rhythmic, contributing to effective gas exchange in the lungs.

Looking at the other options, infrequent and irregular breathing is indicative of abnormalities, such as respiratory distress or certain medical conditions. The presence of retractions around the ribs suggests a struggle to breathe and is commonly associated with respiratory distress, indicating that the person is using accessory muscles to breathe, which is not normal. Similarly, a discrepancy in chest expansion points toward potential respiratory problems or conditions such as pneumothorax, where one lung may not be functioning properly. All these factors differentiate them markedly from the regular, consistent breathing described in the correct answer.