It depends... I don't think you can have the underline before an answer is entered with any question type. However the standard text box entry field should be a reasonable. The Cloze question that Emma mentions, which is awesomely powerful but rather complex. There are some plugins that make it easier to use, one for the old editor
https://moodle.org/plugins/tinymce_clozeeditor
And one for the new
Atto editor
https://github.com/dthies/moodle-atto_cloze
I experimented with that new one recently and it is very nice.
There is my very own Gapfill question type
https://docs.moodle.org/31/en/Gapfill_question_type
That I promote as being very, very easy to use.
MG