The HTML tags that are always nested inside other tags and do not appear by themselves are: c. <li>, d. <td>
In HTML, certain tags are always nested inside others and do not stand alone. \<li\> (list item) is used within ordered (\ <ol\>) or unordered (\ <ul\>) lists, defining individual list items. \<td\> (table data cell) is nested inside \<tr\> (table row) and \<table\>, forming cells within tables.
In contrast, \<a\> (anchor) and \<br\> (line break) can appear independently. \<a\> creates hyperlinks, and \<br\> enforces line breaks. So, \<li\> and \<td\> must be nested, while \<a\> and \<br\> can stand alone in HTML documents.
Therefore the correct options are option C and Option D.
The complete question is:
Which of the following HTML tags are always nested inside other tags and do not appear by themselves?
a. <a>
b. <br>
c. <li>
d. <td>