This offers a great opportunity to do things once only rather than doing them each time the relevant instructions are executed.

这提供了一个很好的机会，可以只执行一次操作，而不必每次都执行相关指令。

youdao

I can't do two things at once.

我不能同时做两件事。

《牛津词典》

Once language starts to develop from about age 2, they do have a system for symbolic representation and can talk about things which aren't in their immediate environment including the past.

一旦语言从2岁左右开始发展，他们就有了一个符号表征系统，可以谈论过去和现在环境之外的事情。

youdao

"People can do things in their own lives, with their children, they can do work in their communities to improve it and once you take those steps, the next logical step is to make sure that your government officials are doing the right thing."

VOA: standard.2010.04.25

But once you get into a situation, it complicates, you see things. How do that happen for you?

但一旦你到了一个环境中，有了具体情况，你就能明白，你是什么情况呢？

普林斯顿公开课 - 人性课程节选

So thankfully, you can do multiple things at once in a program because of what we'll call threads.

因此，谢天谢地，我们在一个程序中可以,同时做几件事情,而每件事情被称为一个线程。

哈佛公开课 - 计算机科学课程节选

You may do things slower, or you may not be able to do things you once did as easily.

CNN: Parkinson's didn't stop his space walk

Have you ever watched someone attempting to do several things at once in the workplace?

FORBES: Why Multitasking Gets You Nowhere, Fast

Just like every family in America, the federal government has to do two things at once.

WHITEHOUSE: Presidential Press Conference on the 2012 Budget