由x2a2-y23=1可知虚轴b=3，而离心率e=ca=a2+3a=2，
解得a=1．
故答案：1．
发型艺术形象的组合因素是创作发型艺术的语言和（）。
A.艺术形式
B.艺术方法
C.艺术手段
D.表现手段
An important reason for constructing an investment policy statement is that it:()
A. minimizes the costs of portfolio construction.
B. ensures that managers outperform the performance benchmark.
C. includes a performance benchmark to judge manager performance.
