Answer:
The 3rd Option
Explanation:
Simple for this question, C: an investigation because it uses only observations.
 
        
             
        
        
        
Atrial fibrillations the problem of irregular heartbeats, due to which clots can form inside the veins, and may lead to stroke, and ultimately, heart failure. An anticoagulant is given to such patients, to decrease the chances of occurrence of a heart attack due to blood clot formation. 
        
             
        
        
        
Answer:
Maximum heart rate
Explanation:
The Maximum heart rate is the number of times your heart should beat per minute during physical activity.
 
        
             
        
        
        
<span> The hypothalamus is the gland in the brain that controls all regulatory activities of the body.</span>