—Excuse me,may I take a seat here? 一____________.The man on the seat has left.
A:You'd better not.
B:No,thanks.
C:Yes,Please.
D:I'm afraid not.
实验材料与用具:适宜浓度的H2O2溶液,蒸馏水,3.5%FeCL3溶液,0.01%过氧化氢酶溶液,恒温水浴锅,试管.
(Ⅰ)设函数f(x)=|x﹣1a|+|x+a|(a>0).证明:f(x)≥2;
(Ⅱ)若实数x,y,z满足x2+4y2+z2=3,求证:|x+2y+z|≤3.
d=8米,圆的周长是( )