Where's my pen? [ ]
A. It's in the desk.
B. It's under the desk.
C. It's on the desk.
答案:B
已知数列{an}的通项公式为an=|n-13|,则满足ak+ak+1+…+ak+19=102的整数k( )
A.有3个
B.有2个
C.有1个
D.不存在
呼吸道的功能是
①进行气体交换②温暖吸入气体 ③清洁吸入空气 ④气体进出通道 ⑤湿润空气
A.①②③④⑤
B.①③③④
C.②③④
D.②③④⑤