stiffness of foot in children

例句：

1. 1. The material is very stiffness.
   这种材料非常僵硬。
2. 2. The chair has a lot of stiffness in it.
   这把椅子有很多硬的部分。
3. 3. The muscles in the arms are quite stiffness.
   手臂的肌肉相当僵硬。