Extrinsic rewards tend to decrease enjoyment of an activity because they answer
a. provide inadequate justification for most activities
b. change our explanation for engaging in an activity
c. are secondary rather than primary reinforcers
d. are negative rather than positive reinforcers

I think the correct answer from the choices listed above is option b. Extrinsic rewards tend to decrease enjoyment of an activity because they change our explanation for engaging in an activity. We became more motivated in getting that tangible reward rather than gaining something internally out of it. 

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.