ad.

1. 在下;向下
   As we flew over the mountains we could see that there were snowy peaks beneath.
   我们飞过群山时看到了底下被雪覆盖着的山巅。
2. (地位等)较低;较劣
   

prep.

1. 在...之下;向...下面
   The sun is now beneath the horizon.
   太阳此刻落到地平线下了。
2. (地位等)低于;劣于
   He is beneath his brother intellectually.
   他在智力方面不如他兄弟。
3. 对...不适合(或不值得)
   He considered that job beneath him.
   他认为做那个工作有失他的身份。
4. 在...影响下