题目

The library ___ here next year will be open to students as well as teachers in our school.   A. set up             B. being set up      C. having been set up    D. to be set up       答案：D4．设△ABC的内角A，B，C的对边分别为a，b，c，且$\sqrt{3}$bsinA+acosB-2a=0．（1）求B的值；（2）若b=2$\sqrt{3}$，求ac的最大值．