For simple sentences, agreement usually isn’t a problem. You can depend on how the sentence sounds to ensure your subject and verb agree.
'The professor requires all students to be in class prior to its start time.'
Here the singular subject professor takes a singular verb requires. Easy! That just sounds correct ....
Legal writers need to create more complex sentences, so relying on our ears won’t always steer us in the right direction. Agreement becomes trickier when subjects become more complex, and writers need to understand some basic agreement rules. [excerpt]
Tenielle Fordyce-Ruff, Back to the Basics: Subject and Verb Agreement, 55(11) Advocate 52 (2012).