Solution:
to solve the above problem. Just use | pipe in the middle of the option value.
<div class="form-dropdown">
<label> Your choice
[select type_exam id:choice_exam include_blank "first-exam | first exam extra text" "second-exam | second exam extra text"]
</label>
</div>
Official doc If you insert a pipe (‘|’) character in the middle of the option value, only the part before the pipe will be open to the outside, and the part after the pipe will be used for mail replacement.