▲本题选D没错，Take it easy 是英语惯用法语，关于其用法，随便查本英语词典都可查到的。如：

朗文词典的解释是：to relax and not do very much 放松; 悠着点

牛津词典的解释是：used to tell sb not to be worried or angry 别急；沉住气；从容点

韦氏词典的解释是：1. to relax and avoid hard work or strain  2. to stay or become calm and unexcited

剑桥词典的解释是：to relax and not use too much energy

▲你的句中的 take it easy 表劝慰，意思是“别急”“别担心”。类似用法如：

Now no use getting fussed. Take it easy! 现在紧张没用，心放开些。

Take it easy. We’ve got him. He’s not going to kill anyone else.  别担心，我们已经抓住他了，他不会再杀人。

▲补充例句：

Just take it easy and tell us exactly what happened. 别紧张，确切地告诉我们发生了什么事。

He is easy to learn English. Just take it easy and tell us exactly what happened. 别紧张，确切地告诉我们发生了什么事。

Just take it easy and tell us exactly what happened. 别紧张，确切地告诉我们发生了什么事。

▲补充说明：take it easy 也可说成 take things easy, take matters easy.