consta={};constb={key:"b"};constc={key:"c"};a[b]=123;a[c]=456;console.log(a[b]);（）[/b][/b] A: 123 B: 456 C: undefined D: ReferenceError
consta={};constb={key:"b"};constc={key:"c"};a[b]=123;a[c]=456;console.log(a[b]);（）[/b][/b] A: 123 B: 456 C: undefined D: ReferenceError
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