I saw the following sentence " This luggage is quite similar to ________." and in the possible answers there were:
A.that one
B.that
I chose A. But the program says the correct answer is B. I don't really get the difference here.
Luggage is a mass (or collective) noun, which describes a number or collection of suitcases, bags, etc. Mass nouns always take singular verbs, which can be confusing.
So, you can say, "This piece of luggage is similar to that one,"
but not, "This luggage is similar to that one."