On the 23rd, during a break in the storm, Lewis and Clark engaged in tree carving activities. Lewis used a special branding iron to mark his name and the date, while Clark carved his name and the date with a knife. Additionally, other members of the expedition carved their initials into nearby trees. According to the author, why was the carving of expedition members' initials on trees significant?
a. It increased their understanding of the plant life of the region.
b. It showed their determination to finish the journey and reach their goal.
c. It helped strengthen American claims to territory in the Pacific Northwest.
d. It demonstrated their desire to follow the customs of the area's Native American tribes.