What is this grammatical rule that applies here? [closed]

So I was doing an elementary level of English language test, and I stumbled upon the following question.

Go past the library, and bus station is opposite _____ the cathedral.

Available answers to this are: a) of b) - (blank) c) from d) to

I answered d) but the woman checking the test said it was supposed to be b) or in other words left blank.

Why is that and whats the rule behind it?

In this case, the word opposite is being used as a preposition and requires no additional preposition. If you said,

The bus station is on the opposite side of the cathedral

you are now using the word opposite as an adjective. In this usage, the preposition of is appropriate to use with the noun side.