Answer:
There are no natural lakes in Maryland, in part because there weren't any glaciers in Maryland during the Ice Age.
Explanation:
The subject-verb agreement refers to a fact that it is a grammar rule that when we are writing a sentence, both subject and verb have to be singular or plural, so they have to agree in number, and that`s how we get the word agreement in this sense.
In the given sentence natural lakes (subject) are in plural form, so the verb that refers to them has to be in the plural too. And as we can see, the verb to be is in its singular form - is, so we have to change it to the plural form are in order to have a correct sentence without errors.
