<em>Entienda</em> is the correct answer leaving the phrase as it follows: <em>Es posible que el estudiante no ENTIENDA la lección. </em>
Explanation:
<em>Entienda </em><em>is conjugated in the subjunctive form (modo subjuntivo)</em>, which is used to express <em>wishes, petitions or possibilities.</em>
The words <em>entenda</em> and <em>entende</em> are misspelled, as mentions the first two options. Whilst the word <em>entiende</em>, as mentions the third option, is written in the indicative form (modo indicativo) which doesn’t express a possibility, but the way how things actually are.
