A、<span lang="EN-US">n</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">＋</span><span lang="EN-US">1</span>
B、<span lang="EN-US">n<span style="mso-spacerun: yes"></span></span>
C、<span lang="EN-US">n</span><span style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">－</span><span lang="EN-US">1<span style="mso-spacerun: yes"></span></span>
D、<span lang="EN-US">1</span>