The correct answer is D. It is neither debatable nor specific.
Step-by-step explanation:
A thesis statement is a set of words that help the author develop and argument. The thesis statement needs to be specific (show a position and reasons) and debatable (it is necessary to provide evidence).
In the case of the thesis statement "Students should be educated" this is not appropriate, because it is neither debatable nor specific. This thesis does not express the position of the author towards education or the reasons why "Students should be educated" which means it is too broad and vague. Also, because it is not specific it is not debatable as there is not any specific point that can be debated or supported.