高手，请谈谈你对这四个词组的理解

at a time: 每次,一次
例句与用法:
1. Female sheep produce one or two lambs at a time.
母羊一次生一到两只羊羔。
2. He tossed the peanuts into his mouth one at a time.
他每次将一粒花生扔进嘴里。
3. If only problems would come one at a time!
要是问题一次只发生一个该多好！
4. He used to abandon his work for months at a time.
他过去每次放下工作就是几个月。
5. Such waste of money should be deprecated at a time like this.
在这种时候应大力反对如此浪费金钱。
6. Personal enmities must be forgotten at a time of national crisis.
民族危机当头, 必须捐弃个人恩怨.

have access to: vt. 可以到达(可以使用)
例句与用法:
1. I have access to his office.
我可以进出他的办公室。
2. Students must have access to good books.
学生必须有机会读到好书。
3. As her private secretary he have access to all her correspondence.
他是她的私人秘书，能接触到她所有的信件。

get across: vi. 通过(渡过,被人了解)
例句与用法:
1. He's not very good at getting his ideas across.
他不善於表达思想.
2. Your meaning didn&#