Answer:
Simple.
Explanation:
In a simple structure of a sentence, there is only one clause with a single subject and also a singe predicate. A predicate is that part of the clause which says something about the verb in the sentence/ clause and also says something about the subject.
The sentence "the rabbits live in the yard but are difficult to find" contains just one subject, which is "the rabbits".
Thus, the sentence is a simple sentence.
