Brenda can remember past just fine but is unable to form new memories. she is experiencing:

Brenda is experiencing the kind of amnesia known as "Anterograde Amnesia".
Anterograde amnesia is lost the capacity to make new memories after the incident or event that caused the amnesia, prompting a fractional or total inability to remember the current past, while long-term memories from before the occasion stay in place.

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.