The orphanage's dreariness is in sharp contrast to the bright smiles of its occupants - more than 40 children, age 8 to 16.
"They were always happy," Cao says.
"Whenever they saw us arrive at the orphanage, they ran to grab our hands and hug us. They were always ready to pose for pictures."
The volunteers played games with the children, who performed African songs and dances for their newfound friends.
Cao says the Chinese students were motivated by a Dutch student, who raised money to build a henhouse so the children can raise hens and sell eggs to make a living.
"After finding out about what the Dutch student did, we brainstormed about what we could do for the children," Cao says.
They decided to help the orphanage acquire legal status and improve the children's living conditions.
1.8 million students have taken NEEP. What motivate them to continue study rather than work?