Which mountain looms are located high above the northern and north eastern boundaries of the expanding city of Tucson?

The Santa Catalina mountains

You should be able to notice the verb loom. Even if you don´t quite understand it, it should be noticeable that it is the verb. Additionally, by skimming the possible answers, one can identify they do not have a verb. Having identified the verb, we can clearly understand we need a subject for this sentence. It is not letter D since the first word is that. It is not letter C since it has the linking verb are, and the verb in the sentences has no -ing ending. It is not letter B since it starts with because. The correct answer is A.