The work of Jonas Salk contributed to the trend shown on this graph
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developing the x-ray machine.

finding safer ways to perform amputations.

introducing a new vaccine.

perfecting the refrigeration of medicines.

states began imposing duties on each other's goods. congress had no way to raise money for an army to expel them.

male citizens in athens could vote on all the decisions that affected the city and serve on juries. however, democracy was not open to everyone. citizen women and children were not allowed to vote. slaves and foreigners living in athens (known as metics) were banned from participating in government.