Which of the following is a valid way to denote a string in many programming languages?

In many programming languages, a string can be denoted using double quotes. The use of double quotes to encapsulate a string allows the programming language's parser to recognize the content inside as a sequence of characters. This is a widely accepted convention in languages such as Java, JavaScript, Python, and C#.

While single quotes are also a valid way to denote strings in several languages (like Python and JavaScript), the focus here is on the specific validity of the double quotes, which is universally accepted in many programming contexts. Additionally, not all languages or contexts recognize the notation "String: Hello" as a valid string representation, as it appears to be a declaration rather than an instantiation of a string value.

Thus, the use of double quotes stands out as a correct and widely recognized method for denoting strings across many programming languages.