Final answer:
The great commercial trail opened for trade between Missouri and New Mexico in 1821 is the Santa Fe Trail.
Step-by-step explanation:
The correct answer to the question is A) Santa Fe Trail. The Santa Fe Trail was a significant commercial highway that facilitated trade between Missouri and New Mexico beginning in 1821. Unlike the other trails mentioned, such as the Oregon Trail and the California Trail, which were primarily migration paths for settlers moving west, the Santa Fe Trail was established as a commercial trade route. Pioneers and traders would travel this route to conduct business, trade goods, and foster economic relationships between the two regions. The trail played a key role in the expansion of the American frontier and in the history of commerce in the early 19th century.