There are two things: 1. Including dynamic content (i.e. by executing some code at the server side to generate new content as opposed to static content such as pure HTML pages).
JSP constructs such as scriptlets are used to generate dynamic content regardless of whether they are included statically or dynamically. A jsp page, whether included statically or dynamically can generate dynamic content. An HTML file, whether included statically or dynamically, can provide only static content.
2. Including content dynamically (i.e. at request time as opposed to statically i.e. compile time). jsp:include (and jsp:forward) action is used to include content dynamically regardless of whether the content is static or dynamic.
If you want to include static content (which is what the question is asking), you can include it statically (option a) as well as dynamically (which the question has not specified) (option c).