Since Mary has a Type A blood, she is either AA or AO while John is either BB or BO. Since both John's parents are Type AB, he can only have the either A or B as an allele and not O so he is BB. Since John can only give the B allele, all of his children must have the B allele in their blood types. So the adopted one is the child with type A blood.
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The source is mainly called headwater and its examples are waterfalls, groundwater, rainfall, and snowmelt in mountains. Basically, it is affected by the gravity
Explanation: