Answer:
3. My uncle, a true cat lover, has had many feline friends over the years.
Step-by-step explanation:
When we have two noun phrases referring to the same word, next to each other in a sentence, we always separate them with commas and this is known as an apposition.
In this case, the first noun phrase is "my uncle" and the second one is "a true cat lover". Since both of them refer to the same person there must be a comma separating them, and also separating them from the rest of the sentence.
For example:
Mr. Francis, my math teacher, turned 58 yesterday.