A:远处学生听到的声音响度大
B:老师发出的声音音色不好
C:远处学生听到的声音响度小
D:老师发出的声音音调低
I have to see the doctor because I ________ a lot lately.
(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.