He behaved as if nothing had happened.

他表现得若无其事。

《牛津词典》

He was marvellously cool again, smiling as if nothing had happened.

他又变得出奇的冷静，微笑着，似乎什么都没有发生过一样。

《柯林斯英汉双解大词典》

"Next day, maybe," the Footman continued in the same tone, exactly as if nothing had happened.

“也许是第二天吧。”仆人继续用同样的声调说，仿佛什么事也没有发生过。

youdao

However, once they are back at work wearing a suit on Monday, it is as if nothing had happened.

FORBES: Side Lines

The government had clearly gambled that Obuchi would be well enough to go back to work on Monday as if nothing had happened.

CNN: Taking Over

Miraculously, by the time we came out of the video and I had to speak again, it was as if nothing had happened.

CNN: Robin Meade talks anxiety and her road to self-confidence