阅读下面的程序,选择正确的答案?( ) class StringDemo{ public static void main(String[] args){ StringBuffer s1 = new StringBuffer("a"); StringBuffer s2 = new StringBuffer("b"); show(s1,s2); System.out.println(s1.append(s2)); } public static void show(StringBuffer s1,StringBuffer s2){ s1 = s1.append("q"); s2 = s2.append(s1); } }