1. The hardness of this diamond makes it one of the hardest substances on Earth.
这颗钻石的硬度使其成为地球上最坚硬的物质之一。
2. The hardness of the math problems frustrated the students.
数学问题的难度让学生们感到沮丧。
3. He is known for his hardness when it comes to enforcing rules.
当涉及到施行规则时,他以其严厉而著称。
4. Despite his physical hardness, he has a kind heart.
尽管他外表看起来强硬,但他内心是善良的。