sand gravel

例句：

1. 1. The beach is covered in soft sand.
   海滩上铺满了柔软的沙子。
2. 2. The construction crew was working with sand and concrete.
   建筑工人正在用沙子和混凝土工作。
3. 3. Sand dunes are formed by the wind blowing across the desert.
   沙丘是由风在沙漠中吹过形成的。