Each winter since 1980, a family measures the snowfall in their yard and records the yearly average. This average is most common when describing what feature of the area A weather
B climate
C water cycle
D erosion patterns

The velocity would be 2 

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.