重点讲解：
1. be discharged from 允许…离开(医院、军队)；
When he was discharged from the hospital, he had lost 20 pounds.
出院的时候，他的体重减轻了20磅。
2. fend off 挡住，抵挡；
Whether this means that we are going to have to fend off recessionary tendencies is not yet clear.
这是否意味着我们将不得不防范经济衰退的趋势，目前尚不清楚。
3. depend on 取决于；根据；由…决定；
Whether or not we can start off tomorrow will depend on the weather.
明日能否出发，须视天气而定。
4. focus on 集中(注意力)；关注；
In this article, we focus on encryption and digital signatures.
本文中我们主要讨论加密和数字签名。