People are less likely to help someone from whom they have already received aid

Tim is studying for a test. After seven consecutive hours of studying, he finds he can remember what he studied five or six hours ago, but he cannot remember what he studied just ten minutes ago. Tim's memory problems are BEST explained by ______

a. proactive interference c. retroactive interference b. memory diffusion d. retrograde amnesia

Hazel was not wearing her helmet when she had an accident on her bicycle. As she fell, her brain was punctured by a broken spoke from the wheel of her bike, causing a rupture of her brain and hemorrhaging. Hazel experiences which type of head injury?

a. concussion c. contusion b. cerebral laceration d. anoxia