Which of the following sentences from the article supports the idea that inventors not succeeding the first time is a good thing?

a
The ROV exercise wasn't a competition, but a self-test of each team's design and maneuvering ability.
b
"I thought we'd come to the pool and everything would work perfectly," said Vivian Kocsis, 12. "It didn't."
c
"A mistake is not the end of the world," said McDonald. "Fixing it builds confidence."
d
Students patiently tackled these problems on-site.