(b) ● 21-1 2-1-1 121 10i 12i (c) 岛 ● ● P号 ● d=0.2225nm d=0.1573nm ● ● ● 0 020 000 020 020 000 020 ● ● ● ● 211 -2-11 ● [101] b=1/2[111] [102]