कि उन्होंने

that they

→ कि
phrase Rare #7,531
that they कि introduces a subordinate clause. उन्होंने means “they” when referring to multiple people or as a respectful form for one person.
HI: मुझे लगता है कि उन्होंने दरवाज़ा बंद कर दिया।
EN: I think that they closed the door.