Choose the Answer Which Best Rewords the Italicized Portion

Multiple Choice

Choose the answer which best rewords the italicized portion. If you think the original wording is best, choose option A.
Etiquette, which is sometimes unwritten, is a code that governs the expectations of social behavior of people.

A) Etiquette, which is sometimes unwritten, is
B) Etiquette, that is sometimes unwritten is
C) Etiquette, that is sometimes unwritten, is
D) Etiquette which is sometimes unwritten is