Dass or das
Das is an article. It is also used as a relative pronoun. For e.g., Das Buch liegt am Sofa. In this sentence, "das" is used as an article. In the sentence, Das Buch, das du liest, gehört meiner Freundin. Here, "das" is used as a relative pronoun.
"Dass," is a subordinating conjunction that is used after the main clause. It is the English equivalent of "that" as in I told my friend that I would meet her.
In German, for e.g., one would use "dass" as follows: Ich denke, dass du Hunger hast. In English, this simply means: I think that you are hungry.
In the following multiple choice exercises you are required to choose das/dass/das ist.