Understanding how to transform sentences between different types is a key part of English grammar. This question asks us to convert an assertive sentence into an exclamatory sentence. Let's break down the process.

Understanding Assertive and Exclamatory Sentences

• Assertive Sentence: An assertive sentence (also called a declarative sentence) makes a statement. It usually ends with a full stop (.). Example: "The sun is shining."
• Exclamatory Sentence: An exclamatory sentence expresses strong emotion or surprise. It usually ends with an exclamation mark (!). Example: "What a beautiful day!"

Transforming Assertive to Exclamatory Sentences

One common way to change an assertive sentence that contains words like "very," "really," or "indeed" before an adjective or adverb into an exclamatory sentence is by using "What" or "How".

• Use "What" when the sentence structure involves a noun phrase (often with an article 'a' or 'an'). The pattern is typically "What + a/an + adjective + noun + !" or "What + plural noun / uncountable noun + !".
• Use "How" when the sentence structure involves only an adjective or an adverb. The pattern is typically "How + adjective / adverb + !".

Analyzing the Assertive Sentence

The given assertive sentence is: "It is a very good idea."

Let's look at the structure after "It is": "a very good idea". This is a noun phrase ("idea") modified by an adjective ("good"), which is further modified by an intensifier ("very"). Since it includes a noun ("idea") and an article ("a"), we expect to use "What" for the transformation.

The structure "It is a very + adjective + noun" is typically transformed into "What a + adjective + noun!".

Evaluating the Options for Exclamatory Form

Let's examine each option provided for the correct exclamatory form of "It is a very good idea."

1. How good idea!

   This option uses "How" but follows it with "good idea". "Good idea" is treated as a noun phrase here. "How" is typically used directly before an adjective or adverb, not a noun phrase with an article like 'a'. Therefore, this structure is grammatically incorrect for transforming the given sentence.

2. What a good idea!

   This option uses "What" followed by "a good idea". This follows the pattern "What + a + adjective + noun!". This structure is correct for transforming an assertive sentence like "It is a very good idea" into an exclamatory sentence expressing strong feeling about the idea.

3. Hurrah what a good idea!

   "Hurrah" is an interjection used to express joy. While it can be followed by an exclamatory phrase, adding it changes the focus from simply transforming the original statement into an exclamation about the idea's quality. It's not the standard direct exclamatory form derived solely from the assertive sentence structure.

4. Good Idea!

   This is a shortened, informal way to express that something is a good idea with exclamation. While it functions as an exclamation, it is not a grammatical transformation following the "What" or "How" pattern derived from the full assertive sentence "It is a very good idea." It omits the subject and verb.

Based on the grammatical rules for transforming an assertive sentence of the form "It is a very + adjective + noun" into an exclamatory sentence, the correct structure is "What a + adjective + noun!".

Correct Exclamatory Sentence

Applying the rule to "It is a very good idea", the adjective is "good" and the noun is "idea". The correct transformation is "What a good idea!".

Comparing this with the options, "What a good idea!" is the correct exclamatory form.

Revision Table: What vs. How in Exclamations

Additional Information on Exclamatory Sentences

Besides using "What" and "How", exclamatory sentences can also be formed in other ways:

• Simply adding an exclamation mark to an assertive sentence to show strong feeling: Example: "I can't believe it!"
• Using interjections at the beginning: Example: "Wow, that was amazing!"
• Using question words in an exclamatory way: Example: "Why was I so foolish!" (Here, "Why" expresses regret or surprise, not asking a question).

The key function of an exclamatory sentence is to convey strong emotion, whether it's surprise, excitement, anger, or joy. When transforming from an assertive sentence that states a fact strongly (like using "very"), using "What" or "How" at the beginning is a common and grammatically standard method.