I’m very grateful to my high school teachers without help I wouldn’t be so excellent.A.

问题补充：

I’m very grateful to my high school teachers, without help I wouldn’t be so excellent.

A. whom

B. their

C. which

D. whose

答案：

A. whom

B. their

C. which

(答案→)D. whose

解析：由逗号可知，这是一个主从复合句的结构，因此可排除B，由后面的help缺少定语可知，应用whose 作定语.而whom which 没有定语的功能，故答案为D

句意为：我非常感谢我的高中老师，没有他们的帮助我不会如此的优秀。