When the artist painted the masterpiece is a real mystery.

Identify the subordinate clause in the sentence.

A) is a real mystery

B) the artist painted

C) the masterpiece is a real mystery

D) When the artist painted the masterpiece

D) When the artist painted the masterpiece

Explanation:

Subordinate clauses can act as an adjective, a noun or an adverb in a sentence.

When the artist painted the masterpiece is a noun clause acting as the subject of the sentence. It is answering the question "What is a real mystery?"

When the artist painted the masterpiece is correct. The subordinate clause is the subject of the sentence.