20. For a reaction: aA → Products, $[\text{A}]_0 = 6.0 \text{ M}$, and the first two half-lives are 56 and 28 minutes, respectively. Calculate $[\text{A}]$ at $t = 105.9$ minutes.
(A) 5.7 M
(B) 12 M
(C) 0.68 M
(D) 0.33 M
(E) none of these

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統計: A(0), B(0), C(1), D(0), E(0) #4064118