Darwin observed the beaks of the birds and how the different beaks helped the birds to eat different types of seeds.
This relates to natural selection because certain finches with say a smaller shorter beak would be able to eat only smaller seeds and fruits as to where a finch with a longer larger beak could eat larger bigger seeds and fruits.
Hope this helped! Have a great day!
Mass number is apart of (what ever subject it is)
Answer:

one atom of an element = 6.02 \times {10}^{23} atom
The mass of one atom of sulphur = 32g
The mass of one atom of aluminium = 27g
so one atom of aluminium = 6.02 \times {10}^{23}
27g of AL = 6.02 \times {10}^{23} atom
2.70g of AL = X atoms
Then you cross multiply ........
and get the answer
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Answer:
A general guideline to determine if oxide is acidic, basic, or amphoteric is to use the periodic table. Typically, metals such as Ba form basic oxides (BaO), while nonmetals such as S form acidic oxides (SO3).