Question

What does “re-use the words of the question (this becomes your thesis)” mean?

Answer 1

Answer:

I think it will mean that the words of the question represent the key-words of your thesis. So you mustn't change the words of the question while writing your thesis

Answer 2

restate the question

for example, if the question was “Was the United States justified in going to war with Mexico?

you would find the answer and restate it

so the thesis would be

yes (or no) the United States was(n’t) justifies in going to war with Mexico.