A.4π              B.2π        C.              D.π

椭圆的焦点在轴上，长轴长是短轴长的两倍，则的值为（     ）

A.  4                 B. 2                    C.                D.

已知正实数x₁,x₂及函数f(x),满足4^x=,且f(x₁)+f(x₂)=1,则f(x₁+x₂)的最小值(    )

A.4            B.2           C.               D. 

设满足约束条件 ，若目标函数的最大值为4，则的值为(    )

A. 4                     B.2                      C.                       D. 0

A.4                  B.2                 C.                D.