Final answer:
Thomas Jefferson assigned Robert Livingston and James Monroe to negotiate the Louisiana Purchase with Napoleon's France, resulting in the U.S. doubling its territory. Hence, the correct answer is option (b) and (c).
Step-by-step explanation:
Thomas Jefferson chose Robert Livingston and James Monroe to negotiate the Louisiana Purchase. These negotiations were with France, under the rule of Napoleon Bonaparte, who was willing to sell the territory due to his need for funds after the failure of his plans in Haiti.
The purchase agreement, known as the Louisiana Purchase Treaty and Conventions, was signed in Paris on April 30, 1803, effectively doubling the size of the United States for the sum of $15 million.