Thanks to Liu's tireless efforts, her son could make some sound after several months of training, and her students showed great improvement. "Whenever they managed to say 'mom' or 'dad' for the first time, I felt it was the sweetest sound in the world," she said.

Studies show that children with hearing difficulties can learn to speak, even though the process is very difficult. But for that, treatment should start early, she said.

Deng Liang, who is 43 today, was one of Liu's first students. He was 10 years old when he went to the school but had not learned how to speak till then. With the help of Liu and hearing aid, he can now understand basic conversation and speak using simple words. And he has worked really hard to receive higher education with the help of the teachers.

After graduating from Tianjin University of Technology in 2007, Deng started working for a State-owned enterprise in Changsha. "Mrs Liu taught me to be kind, optimistic and work hard to build a better life, which has motivated me all these years," he said.

Deng's wife Jiang Yan, too, is one of Liu's former students. After Jiang was admitted to the special education school, she tightly held on her mother's clothes and did not want her to go. Liu held her up gently to calm her down, just like a mother, which Jiang remembers vividly.

In school, Jiang played with other students and learned how to speak. She said Liu would demonstrate more than 100 times how to speak just one syllable. After graduating from the school, she enrolled in a high school and was later admitted to the Beijing Union University. And after graduating from college, she became a teacher for special children.

Liu Hanxiang came to Liu Lingli's school when she was 8 years old. As she rarely tried to speak before joining the school, her vocal cords had become very stiff. So Liu Lingli started helping her practice speaking every day and after several years of efforts, Liu Hanxiang could communicate normally with others.

The teacher also encouraged her to learn dancing and she was enrolled in the China Disabled People's Performing Art Troupe. After performing during the celebrations to mark the establishment of diplomatic ties between China and Panama in 2017, Liu Hanxiang sent a text message to her teacher and mentor thanking her for her efforts.

"Mrs Liu, my performance today was a great success. I want to thank you. Without you, I would not have become who I am today," the message read. Liu Lingli burst into tears when she read the message.

For her contributions to society, especially her work with the hearing-impaired, Liu Lingli was elected as a deputy to the National People's Congress last year, and fulfilled the heavy responsibility of speaking for people with disability.

There is still a lot to do to ensure disabled people can find suitable jobs or start a business. For example, the government could issue more diversified and flexible policies, Liu Lingli said. The media also needs to more prominently tell the stories of people with disability who have built a successful career, so as to motivate children with disability to improve their lives through learning.