As soon as he finished his speech, there was spontaneous applause from the audience.

Answer: Option C

well-timed : occurring at an appropriate time; timely.
willing : ready, eager, or prepared to do something.
instinctive : (of a person) doing or being a specified thing apparently naturally or automatically.
instantaneous : occurring or done instantly.
spontaneous : performed or occurring as a result of a sudden impulse or inclination and without premeditation or external stimulus.


Synonym of spontaneous is instinctive