Which nitrogenous base is normally present in rna
molecules but not in dna molecules?
(1) adenine
(3) thymine
(2) cytosine
(4) uracil

  In DNA, the pyrimidine cytosine always pairs with the purine guanine, while the pyrimidine thymine always pairs with the purine adenine. RNA does not contain thymine, though, so in RNA adenine pairs with uracil.

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.