Belong

Belong is not an adjective; it is an intransitive verb that cannot be used in the passive voice and is never used in the progressive tenses, so it should never be preceded by a to be verb. To quote an Internet meme:

all your bases are belong to us

all your bases belong to us

For native Chinese speakers learning English as a second language, the usage of belong presents a particular challenge (and is often misunderstood) because the Chinese expression usually equated with the English expression belong to (属于) is typically used with a to be verb (是):

你所有的基地是属于我们的。