Her smile always hang/hanging on her face?

答案解析：不能用现在分词;因为现在分词属于非谓语动词,不能做句子谓语,因此要用一般现在时态,也就hangs

Her smile always hangs on her face

主句：Her smile

谓语：hangs

状语：always

状语:(2) on her face (地点状语)

中文意思：她的笑容一直挂在她的脸上