Which of the following is a reason that normal vital signs can change?

Normal vital signs can change due to a variety of factors, and each of the reasons provided contributes to this variability. Exercise significantly impacts vital signs, as physical activity can lead to increases in heart rate and respiratory rate, along with temporary changes in blood pressure as the body works to supply more oxygen to muscles.

Health conditions also play a critical role; conditions such as fevers, infections, and chronic illnesses can lead to notable deviations from baseline vital sign ranges. These changes occur due to the body's response to maintain homeostasis or react to underlying physiological processes.

Moreover, sex can influence vital sign measurements as well. Research indicates that males and females may exhibit differences in baseline heart rates, blood pressure readings, and temperatures due to genetic, hormonal, and anatomical factors.

Considering that all of these factors—exercise, health conditions, and sex—contribute to changes in vital signs, it is accurate to conclude that the correct answer encompasses all of these influences.