To ensure that your research project is manageable, you must be sure that your topic is historical, so there will be plentiful sources narrow enough to be presented thoroughly broad enough for the audience to relate to on something you feel strongly about

Hi there!

I believe that the words that fit better to fulfil your sentences are not historical, but narrow enough to be presented thoroughly.

To ensure that your research project is manageable, you must be sure that your topic is narrow enough to be presented thoroughly.

Even though selecting a good topic may not be easy, there are some things to have in mind, such as the topic must be narrow and focused enough to be interesting, yet broad enough to find adequate information. It is also important to make sure to know how the final project will look like before selecting your topic.

Hope this helps!

the answer is definitely d. sorry for a late response.