—Shall we go to the amusement park right away or next weekend? — ______Any time will do.
A:Excuse me.
B:Have a good time .
C:I'm afraid I can't
D:It's up to you .
已知等差数列{an}中共有18项,其中奇数项之和为11,偶数项之和为29,则其公差为( )
无论各种鸟的生殖和发育有何特点,在生殖和发育过程中,鸟必须具有哪几种行为( )