"in pavlov's experiment on classically conditioning salivation to a sound, what procedure produces spontaneous recovery? "

From the experiment, spontaneous recovery was seen when the sound was presented without the food, and then the trial was done again with the food after a long period of time.

The correct answer is a. when they started making tools that will them in cultivating lands, they could raise crops and that made them attached to one place for a longer period of time. after that, they started domesticating animals and building their own permanent settlements that resemble the ones we have today.