Of course they have. Otherwise with the growth of their economy and trade, the value of their currency would have skyrocketed vs the dollar. Good thing you didn't teach economics. They purposefully devalue their currency to undercut prices worldwide and subvert manufacturing in other countries.
How else do you explain a Yuan vs the dollar of 7 +/- 15% since 1990. Despite a 4200% increase in their GDP.
In that time they went from nothing to the 2nd largest economic power in the world and 1st in manufacturing.
And you think their currency would not gain value against the dollar? Glad you didn't teach economics.