17. 平衡下列化學反應式後,各物質係散總和為何?
$\text{NH}_3(\text{g}) + \text{O}_2(\text{g}) \rightarrow \text{NO}_2(\text{g}) + \text{H}_2\text{O}(\text{g})$(A) 6(B) 14(C) 17(D) 21