Given:class CardBoard {  Short story = 5;  CardBoard go(CardBoard cb) {    cb = null;    return cb;  }  public static void main(String args) {    Car

Given:class CardBoard {  Short story = 5;  CardBoard go(CardBoard cb) {    cb = null;    return c

b;  }  public static void main(String args) {    CardBoard c1 = new CardBoard();    CardBoard c2 = new CardBoard();    CardBoard c3 = c1.go(c2);    c1 = null;    // do Stuff  } }When // doStuff is reached， how many objects of CardBoard are null?

A:0
B:1
C:2
D:Compilation fails.
答案: 2

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