+12 = 20 

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  1. 鍛鍊文選·張協·》:。」

  2. (protactinium,Pa)​化學元素原子序91。放射元素銀灰礦物化學證實

protactinium (chemistry)​
protactinium
Protactinium (Element 91, Pa)​ (S, Chem)​