4 structures of underside of the leaf
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chert is a sedimentary rock composed of microcrystalline or cryptocrystalline silica. with this little bit of information, you can come to the conclusion that your answer is c.  

explanation:

i believe it's c. the trait for large beaks will be passed on to future generations through natural selection.

since eventually smaller beaks would have to find another source of food or even eventually just die out from the lack of food.