What is the correct syntax for declaring a variable?

The correct syntax for declaring a variable in JavaScript typically follows certain conventions regarding naming and keyword usage.

The option where "let last_name" is provided uses the "let" keyword, which is a valid way to declare a variable. In this case, "last_name" is a perfectly acceptable variable name, although camelCase is more commonly used in JavaScript for variable names (e.g., lastName).

The use of "let" allows you to create block-scoped variables, which can be beneficial for managing variable scope within functions or blocks. This contrasts with "var," which has function scope and can lead to variable hoisting issues.

In summary, the option using "let" correctly reflects how modern JavaScript variables can be declared, showing not only an understanding of syntax but also the preferred use of variable declarations in contemporary JavaScript coding.