The system of Braille is really to the blind.A. of great usefulB. great usefulC. great us

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。