Read the excerpt from The Boy Who Harnessed the Wind by William Kamkwamba. A sudden gust muffled the voices below, then picked up into a steady wind. It took hold of my T-shirt and whistled through the tower rungs. Reaching over, I removed a bent piece of wire that locked the machine's spinning wheel in place. Once released, the wheel and arms began to turn. They spun slowly at first, then faster and faster, until the force of their motion rocked the tower. My knees buckled, but I held on.

Which character trait do the details in the excerpt reveal about Kamkwamba?

a. curiosity
b. empathy
c. loyalty
d. determination