To answer this question, you need to understand the naming convention for scalar variables in Perl.
Option A) # - This option is incorrect because the # sign is used to indicate comments in Perl, not for naming variables.
Option B) @ - This option is incorrect because the @ sign is used to denote arrays in Perl, not for scalar variables.
Option C) % - This option is incorrect because the % sign is used to denote hashes in Perl, not for scalar variables.
Option D) $ - This option is correct because scalar variables in Perl always begin with the $ sign. Scalar variables hold single values, such as numbers or strings.
The correct answer is D. This option is correct because scalar variables in Perl are always denoted by the $ sign.