Boris Yeltsin struggled to improve the economy, he emphasized transitioning to a free-market economy.
He struggled to improve the economy, and economic problems led to a political crisis, as well as the war in Chechnya.
Transitioning to a free-market economy was a major challenge for Soviet President Boris Yeltsin in the 1990s.
Therefore, option D explains the challenge for the Soviets in the 1990s.
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