It had become an issue since the cloning of Dolly the sheep in Scotland.

自苏格兰的多利羊被克隆后，这已成为一个争议性问题。

youdao

By the evening it had become unbearably hot.

到了晚上天气已热得无法忍受。

《柯林斯英汉双解大词典》

Before long, it had become a beautiful little park.

不久，它就变成了一个美丽的小公园。

youdao

It was the largest seaport. It had become a busy industrial center, producing war equipment for Confederate forces.

VOA: special.2009.09.10

It was then in a matter of moments, that I decided that I had to find out why and become happier.

也就是在那时，我决定要找出原因，变得快乐。

哈佛公开课 - 幸福课课程节选

It had become free territory under the Missouri Compromise.

VOA: special.2009.05.14

Off-limits to foreigners during the Cold War because of its military bases, it had become accessible again.

FORBES: Catch and Release

In fact, it had become arguably the most gangster-ridden major industrial company in Russia.

FORBES: The Rise Of An Oligarch

By the 1950s it had become increasingly clear that not everyone could afford the contributions.

BBC: Beveridge report: From 'deserving poor' to 'scroungers'?