It`s a matter of subject-verb agreement in this independent clause: «The overall security of the city has improved significantly since it was hired.» To simplify, the subject is «security», which is a singular noun, so the verb must also be singular, which «has improved» hurts and «improved» the corrected verb. So we found that subject-verb concordance questions can be difficult, because the subject is often not placed right in front of the verb. Let`s see how it goes with a real ASA question. Let`s first look at a sentence with a sentence that pauses. If you answer these kinds of questions, remember that nouns must match their corresponding verbs, and both must be singular (in relation to one thing) or plural (referring to more than one thing). The theme of the sentence is «Changes» and the prepositional sentence provides descriptor information about the changes. Since the subject is plural, the verb should be in the plural form. Do you know how to conjugate the verb to combine it with the theme in foreign languages? We have the same thing in English, and it can become difficult, even if simple cases seem so natural and obvious to us: the tricky part of the example is that the noun closest to the verb is the plural «friends», so it may seem fair to say «to be friends». But what is part of the family tradition is not the friends, but the «letter», which is singular. Therefore, the corresponding verb should also be the singular «is». To determine the topic, think about what is simple. We also know that «of all the Kardashian sisters» is a prepositional phrase that we can remove and will not contain the subject.
So we are left with «The memory of names is simple».