'We know that the earth is a planet'. The underlined part is a/an— (49th Special BCS)

Clause identification is a fundamental skill in English grammar for BCS examinations. Sentence Analysis: "We know [that the earth is a planet]" — Main clause: "We know" — Subordinate clause: "that the earth is a planet" Why it is a Noun Clause: 1. The clause "that the earth is a planet" functions as the OBJECT of the verb "know" 2. You can ask: "We know WHAT?" → "that the earth is a planet" — this answers "what", making it a noun 3. A Noun Clause performs the function of a noun (subject, object, or complement) Noun Clause test: Replace the clause with a pronoun: "We know [it]" — Yes, "it" can replace the clause → It is a Noun Clause Distinguishing clause types: ✗ Adverbial Clause: Answers when? where? why? how? (e.g., "She left because it was late.") ✗ Adjective Clause: Modifies a noun (e.g., "The book that I read was great.") ✗ Principal Clause: The main/independent clause ("We know") — the underlined part is subordinate Other Noun Clause connectors: — That, what, who, whom, whether, if, how, when, where, why Source: English Grammar in Use — Raymond Murphy; A Practical English Grammar — Thomson & Martinet.