What is a Predicate Adjective Example?

Hello, and thank you for your question.

An adjective is something that describes a noun. A predicate adjective is an adjective that follows a linking verb and describes the subject of the sentence. Let's break down example A:
The cake smells delicious - 'The cake' is the subject/noun - 'smells' is the linking verb - therefore 'delicious' is the predicate adjective. 
Breaking down the other examples in the same way, will help you identify the predicate adjectives 'stunning', 'warmer' and 'brilliant'. 

I hope that this explanation has helped you.