问题补充:
The system of Braille is really to the blind.
A. of great useful
B. great useful
C. great use
D. of great use
答案:
A. of great useful
B. great useful
C. great use
(答案→)D. of great use
解析:句意:盲人系统对盲人真的是有用的。这里使用be of+抽象名词=形容词,great是形容词修饰名词use,of great use=very useful,所以选D。