Lin Wenchu, head of the laboratory-animal center. [Photo provided to China Daily]

Students were asked to hold their national flags at an "international day" event at their daughter's school. But Zhang Xin found that her daughter could not identify China's flag.

And when she spoke to her daughter in Chinese at home, the girl would always reply in English.

"Now her Chinese has improved, and she can recite many Chinese poems," says Zhang Xin.

Zhang Na headed for Brigham Young University in Utah in 1996 to earn his master's, before going to Cornell University's Weill Cornell Medicine school in New York for doctoral studies in 1998.

During US presidential elections, he usually found himself debating with people about issues regarding China.

"Presidential nominees always fight for votes by raising unfair arguments about China. So I had to speak up for my country," says Zhang Na.

"For that reason, I always read news about China online. So when I argued, I argued with facts and evidence."