Question

Combine the following sentences into a complex sentence with a subordinate noun clause:
The Earth is round. Everyone knows it. [Advanced]

• A. The Earth which is round is known to all.
• B. Everyone knows where the Earth is round.
• C. That the Earth is round is known to all.
• D. Everyone has the knowledge of the Earth being round.

Answer 1

The correct option is C That the Earth is round is known to all.

A Complex Sentence consists of one principal clause and any number of subordinate clauses.
A Noun Clause is a subordinate clause which does the work of a noun in a complex sentence.
In this case,
Option C is correct. The subordinate clause That the Earth is round acts as the subject of the verb is known in the principal clause. The subject is always either a noun or a pronoun. Henceforth, That the Earth is round is a subordinate noun clause as it behaves as a noun.
Option A is incorrect as the sentences have been joined by a subordinate adjective clause where the noun The Earth is being described.
Option B is incorrect as the sentences have been joined by a subordinate adverb clause which modifies the verb 'knows' in the principal clause.
Option D is incorrect as it's a simple sentence.