The corrected sentence is: “A pair of support shoes is important if you are suffering in your lower back.” The theme of the second part of the sentence is “each of its other qualities”. Here, the subject is singularly due to the modifier “each”. To make this easier to understand, try reading this part of the sentence as “each of its other properties.” Therefore, the corresponding verb must be available in a form that can be used with a singular noun, “compensated”. The same principle applies when the names in the subject do not change in number, but in person. In the example below, the subject consists of a third-person subject (Amelia) and a first-person pronoun (I): The examples also show that if the subject contains both singular and plural nouns, the more natural normally seems to place the plural last closest to the verb.