spontaneous abortion

词形变化：

副词: spontaneously | 名词: spontaneousness |

同义词：

instinctive | natural | automatic | inherent | extemporaneous | involuntary | voluntary | option | impulsive | unprompted | spur-of-the-moment | artless | unstructured | unplanned | free | unrehearsed | unconstrained | ad-lib | self-generated | unwritten |

反义词：

induced | compulsory |