what's the different use KeepAlive and "httpclient.reset_state_on_thread_group_iteration" in jmeter5.0's jmeter.properties

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hello ??
i need something help :
i want to know what's the different use KeepAlive and 
"httpclient.reset_state_on_thread_group_iteration"  in jmeter5.0's 
jmeter.properties