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The correct option would be B. consent can be obtained from adult stem cell donors. 
The controversy behind the other option is that it is a form of life, but no consent is taken from the actual life. (i know it's phrased weirdly, my bad)
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Xylem and phloem fiber cells
        
             
        
        
        
Hello! THere are many differences between a grassland and a savanna. For one, a savanna is a grassland, however, A savanna is usually very dry. A savanna also has very few trees, while grasslands can be plush with many trees. Grasslands could also be in mountains while savannas are vast dryer lands with animals who live in dry weather. Grasslands also contain a lot of water sources like lakes, rivers, ponds, and savannas usually don't. Those are just a few o the many differences between them! 
I hope this helped!
I am, yours most sincerely,
SuperHelperThingy
        
             
        
        
        
interlocking calcium carbonate plates is the answer.