What social changes were most responsible for the 30-year increase in American life expectancy over the 20th century?

answer is given below

Explanation:

Social change refers to any significant change in behavior patterns and cultural values and norms over time

so for 30 year in america they are as

these were the some change

texas governor sam houston opposed secession, but was unable to prevent it. in this speech, given prior to lincoln's election, he presents the argument that slavery would be safer within the united states than outside of it. it was a prescient argument, and one held by several other southern leaders.

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answer; they both highlight the power of the situation in determining behavior;