Declarative long-term memories are unavailable to the consciousness. are implicit memories. are usually caused by classical or instrumental conditioning. can be expressed verbally. do not involve the hippocampus.

The correct answer is can be expressed verbally. 

Declarative memories refer to explicit long-term memories of facts, learned knowledge and events, that can be consciously recalled. Examples of declarative memory include knowing who the first president of the United States was, the age at which you learned how to ride a bicycle and your mother's birthday. 

The changes to agriculture in the united states since 1900 is that increased mechanization has increased food production, thereby increasing the need for labor. there has been an increased need for higher speeds of food production due the fact that the population in the united states continues to rise.