Final answer:
A sentence with a subordinate clause functioning as a modifier to the subject provides additional information about the subject.
Step-by-step explanation:
An example of a sentence with a subordinate clause functioning as a modifier to the subject is:
The student who always studies diligently scored the highest mark on the test.
In this sentence, the subordinate clause 'who always studies diligently' modifies the subject 'The student' by providing additional information about the student's studying habits.