The sentence that contains a compound subject is B. Their friends and relatives from Austria visit often.
Explanation:
The subject of a sentence is the person, thing or idea that carries out the action defined in the predicate. When the sentence has two or more subjects, that subject is called <u>compound subject</u>. In a <u>compound subject</u>, the individual subjects are joined by a coordinating conjunction, such as <em>and</em>, <em>or</em>, etc. In this case, the individual subjects that form the compound one are <em>their friends</em> and <em>relatives </em><em>(from Austria.)</em>
