硬质

例句：

1. 1. The material is very hard to work with.
   这种材料很难加工。
2. 2. The rocks are hard and unyielding.
   这些岩石很硬且不易变形。
3. 3. The car was so hard to start that I had to call a mechanic.
   这辆车启动太难了，我不得不叫来修车工。