JavaScript ES6 modules are implicitly in strict mode. There is no need to add the "use strict"; directive. This design choice helps create more robust and maintainable code by preventing common errors and enforcing better coding practices. You cannot opt out of strict mode for modules; any code within a module file is automatically parsed in strict mode by the JavaScript engine.

A. use non-strict; is not a valid JavaScript directive. There is no way to disable strict mode within an ES6 module.

C. use strict = false; is not a valid JavaScript statement or directive for controlling strict mode.

D. The concept of notStrict() functions is not a feature of JavaScript. Strict mode applies to the entire module's scope.

1. MDN Web Docs, "JavaScript modules", Section: "Other differences between modules and standard scripts". It states, "Modules are automatically in strict mode... There's no way to opt-out of strict mode for modules."

2. ECMAScript® 2015 Language Specification, Section 15.2.1.8 "Module Semantics". The specification dictates that module code is always evaluated as strict mode code.