A. 無法確定
B. public boolean equals(Object o) { Sock s = (Sock) o;return size.equals(s.size); }
C. public boolean equals(Object o) { Sock s = (Sock) o;return color.equals(s.color); }
D. public boolean equals(Object o) { Sock s = (Sock) o;return size.equals(s.size) &&color.equals(s.color); }