Answer: Antigens
Explanation: The ABO system of blood grouping is based on the basis of the type of antigens that are present in the red blood cells. Erythrocytes is another name for the red blood cells. Antigens are molecules that are capable of eliciting immune response. There are two types of antigens: antigen A and B. Blood type A has only antigen A, blood type B has only antigen B, blood type AB has both antigen A and B while blood type O has no antigen (neither A nor B antigen). 
Similarly, Rh trait is determined by the presence or absence of rhesus antigen in the erythrocytes. Rhesus antigen is an antigen first discovered in rhesus monkey. Rh+ indicates the presence of rhesus antigen in the red blood cells while Rh- indicates the absence of rhesus antigen in the red blood cells.
 
        
             
        
        
        
85% of adults are grandparents by age 65. This estimation has been made in the U.S. from the surveying of the elderly. So, the correct choice is the third option: 85. 
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                - Dotz
        
             
        
        
        
The ocean floor regions are the continental margins, the ocean basin floor, and the mid-ocean ridge.
        
                    
             
        
        
        
Answer:
 b. epinephrine on beta 2 receptors causes bronchodilation
Explanation:
This is because epinephrine is an hormone and neurotransmitter that stimulate beta 2 receptors which causes signaling and their in presence in airway smooth muscle causes bronchodilation, which counter the activation of the M3 muscarinic receptors in cardiovascular. When stimulate in skeletal muscles it can lead to increased contractility and also to muscle tremors.