The correct answer is (a) <summary>
Easiest explanation: The <summary> tag is new in HTML5. <summary> element defines a visible heading for <details> element. This heading can be clicked to hide/view the details. This element is not supported by Internet Explorer. Sections in document is defined by <section> element. <mark> element is used to highlight the context/paragraph/text. Main content of document is specified by <menu> element.
