| A | B |
|---|
| social | living together in communities or groups |
| exchanges | a giving of one thing for another |
| excess | more than is needed or usual |
| reinforce | to make stronger with more material, help, or support |
| storage | a space or place for storing things |
| transport | to carry from one place to another |
| chamber | an enclosed space in a machine or in an animal's living space; compartment |
| scarce | not enough to meet a demand |
| obstacles | something that blocks or stands in the way |
| transfers | to cause to move from one place to another |
