spontaneously

观众们突然自发地鼓起掌来。

The audience ___spontaneously burst into applause.

孩子们看到彩虹后，自发地欢呼起来。

The children cheered ___spontaneously when they saw the rainbow.

我们突然决定去海边野餐。

We ___spontaneously decided to have a picnic by the beach.