24. Naturally occurring copper exists in two isotopic forms: 63Cu and 65Cu. The atomic mass of copper is 63.55 amu. What is the approximate natural abundance of 63Cu?
(A) 70%
(B) 63%
(C) 90%
(D) 50%
(E) 30%

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統計： A(33), B(3), C(2), D(1), E(0) #2020328