spontaneously

自发发生

used especially in scientific or formal contexts for events that happen naturally

尤其用于科学或正式语境中，指自然发生的事件

自发地发生

to describe events that occur without planning or external cause

描述未经计划或没有外部原因而发生的事件

自发反应

to respond to a stimulus without conscious thought or pre-meditation

无意识或未经预想地对刺激做出反应

自发出现

for problems or situations to appear without a clear cause

用于问题或情况在没有明确原因的情况下出现

自发爆发

to begin suddenly and with great force, like a volcano or conflict

突然并猛烈地开始，如火山或冲突

自燃

to catch fire without an external source of ignition

没有外部火源而着火

to be created or produced without an external agent, often in a biological or abstract sense