To answer this question, you need to understand the differences between System.Text.StringBuilder and System.String in terms of mutability and efficiency.
Option A) StringBuilder is more efficient when there is a large amount of string manipulation - This option is correct. StringBuilder is designed to be more efficient when there is a need for frequent string manipulation. It provides methods to modify the string without creating a new instance in memory each time.
Option B) Strings are immutable, so each time a string is changed, a new instance in memory is created - This option is correct. System.String objects are immutable, meaning they cannot be changed once created. When you modify a string, a new instance is created in memory.
Option C) StringBuilder is mutable; when you modify an instance of the StringBuilder class, you modify the actual string, not a copy - This option is correct. StringBuilder objects are mutable, meaning they can be modified without creating a new instance. When you modify a StringBuilder object, you modify the actual string it holds.
Option D) Strings are mutable in .Net - This option is incorrect. Strings are immutable in .NET. Once a string is created, it cannot be changed. Any modifications to a string result in the creation of a new string instance in memory.
The correct answer is D) Strings are mutable in .Net. This option is incorrect because strings are actually immutable in .NET.