The complete subject of the following sentence is and the simple subject is
This old radio works very well.

The complete subject of the following sentence is __old radio

the simple subject is _radio

Explanation:

old is the modifier

A simple subject is the main word or words in a subject. It does not include any of the modifiers that might describe the subject. To identify the simple subject in a sentence, ask yourself who or what performs the action in the sentence. Remember, though, that a simple subject is very basic.

buenas noches would be your answer