Unergative verbs have a single argument that characteristically bears the thematic role of agent and occupies the subject position.
mai4 jiu3 de0 ren2 xiao4 le0 liu2 jia1 de0 ren2 ye3 xiao4 le0
sell wine DE person smile LE Liu family DE person also smile LE
‘The wine vendor smiled, and the Lius also smiled.’
Li, Y.-H. Audrey. 2016. Verbs and verb phrases. In A Reference Grammar of Chinese, eds. by Chu-Ren Huang and Dingxu Shi. Cambridge University Press.