This sentence is from The Economist. I am confused with the usage of "at which"，I don‘t know what “which” means.Thanks!
According to the Centres for Disease Control and Prevention (CDC) overall life expectancy fell for the second time in three years in 2017, driven by a surge in opioid overdoses and suicide(自杀), at which whites are most at risk.
According to the Centres for Disease Control and Prevention (CDC) overall life expectancy fell for the second time in three years in 2017, driven by a surge in opioid overdoses and suicide(自杀), at which whites are most at risk.
