steep coal seam

例句：

1. 1. The mountain was so steep that it was hard to climb.
   那座山太陡了，很难攀登。
2. 2. The river is very deep and the current is strong.
   这条河非常深，水流湍急。
3. 3. The cliff was steep and we had to use ropes to climb down.
   悬崖很陡，我们不得不使用绳索来下爬。