问题
选择题
—______,do you have a ruler?
—Yes, here you are. [ ]
A. Sorry
B. Excuse me
C. Hi
D. Pardon
答案
答案：B
搜题请搜索小程序“爱下问搜题”
—______,do you have a ruler?
—Yes, here you are. [ ]
A. Sorry
B. Excuse me
C. Hi
D. Pardon
答案：B
，且
。
是log2an和log2an+1的等差中项，求数列
的前2n项和。