Shouldn't you add PROBABILITY in the HINT section. Instead of "deber" why does it not say "deber de"?

Question

-¿Sabes dónde está la abuela? -________ café con sus amigas.-Do you know where grandma is? -She must be having coffee with her friends.(HINT: use modal verb "deber" and the verb "tomar" for to have)
According to Kwiziq the correct answer is "Debe de estar tomando café con sus amigas." Or are we supposed to understand the difference from the question and the answer?

Accepted Answer

Hola Joanne
I imagine you are referring to either deber or deber de, so you would want to see the word "possibility" in the hint. However, for "assumptions", both deber and deber de are correct, so you can answer "debe estar tomando" and "debe de estar tomando" - both answers set as correct in the system. Have a look here.
I hope this clarified it.
Saludos