Identify the clause of the highlighted part in the given sentence.
We must never forget that honesty is the best policy.

Correct option is C

The correct answer is (c) Noun Clause.
The highlighted part “that honesty is the best policy” acts as the object of the verb forget. Since it performs the function of a noun in the sentence, it is identified as a noun clause.
• Grammatical rule involved (English):
A clause that works as a subject or object of a verb is called a noun clause. Such clauses are often introduced by that, whether, or if.
• व्याकरण नियम (Hindi):
जो clause वाक्य में noun का कार्य करता है (subject या object के रूप में), उसे Noun Clause कहा जाता है। That से शुरू होने वाले clause अक्सर noun clause होते हैं।
• Meanings / role of the other options:
• (a) Adverb Clause: Modifies a verb, adjective, or adverb.
• (b) Principal Clause: The main clause is We must never forget.
• (d) Adjective Clause: Modifies a noun, which is not the case here.
Thus, the correct option is (c).