I can use this background: Circadian rhythms are regular changes in biology or behavior that occur in a 24-hour cycle. In humans, for example, blood pressure and body temperature change in a regular way throughout each 24-hour day. Animals may eat and drink at certain times of day as well. Humans have daily cycles of behavior, too. Most people start to get sleepy after dark and have a hard time sleeping when it is light outside. In many species, including humans, circadian rhythms are controlled by a tiny structure called the biological clock . This structure is located in a gland at the base of the brain. The biological clock sends signals to the body. The signals cause regular changes in behavior and body processes. The amount of light entering the eyes helps control the biological clock. The clock causes changes that repeat every 24 hours.  Now, I have a new situation: Marcus has a long day ahead of him. He woke up early, around 7 AM to start his day. For a research study he takes his blood pressure around 9 AM and continues on through his day. Around noon he takes his blood pressure again noting that it has increased a little. He takes his blood pressure one more time before going to bed around 10PM  Answer this question please: Will an animals blood pressure be at its highest in the middle of the day or at its lowest?
A:
highest