A.a,b,c全为正数               B.a,b,c全为非负实数

C.a+b+c≥0                    D.a+b+c＞0

A.          B.a²+b²              C.2ab          D.a

A.=                           B.＜

C.=且＜         D.=或＜

A.10           B.11          C.12           D.13

A.2ab＜＜＜b

B.2ab＜＜＜b

C.＜2ab＜＜b

D.2ab＜＜b＜

A.c≥b＞a                      B.a＞c≥b

C.c＞b＞a                      D.a＞c＞b

A.xy＞yz                          B.xz＞yz

C.x|y|＞z|y|                     D.xy＞xz

A.a+＞b+                 B.＞

C.a-＞b-                  D.＞

(1)求f(x)的单调区间;

(2)若a＞b＞0,c=.

求证:f(a)+f(c)＞.