What forced russia to discontinue fighting in world war i?

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It was poorly supplied, trained and led.
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It was no match for the modern German army and it suffered great losses.
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This led to widespread unrest in the ranks of the soldiers.
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Soldiers deserted by the thousands.
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Soldiers shot their own officers.
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Soldiers formed committees within their own units to decide what they would do on the battlefield rather than just take orders.
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The common soldier welcomed the Bolshevik revolution since it put Vladimir Lenin in position to end the war.
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Your answer should be choice b!