1) Have you ever heard of a Stradivarius violin? (2) It is a type of instrument that was built by members of the Stradivari family in Italy during the 1600s and 1700s. (3) They used a variety of wood and secret methods to create different instruments, and about 650 of their violins still exist today. (4) Some musicians, who play Stradivarius violins, refuse to use any other.

Which sentence contains an error in the use of a restrictive clause?

How could you correct this error?