Answer:
A. In-depth historical data
Step-by-step explanation:
When starting a new research project you should always gather in-depth historical data. This form of data will provide you with a wide array of information that other individuals have already gathered and documented regarding the specific topic that you are currently researching. Aside from providing you with valuable information it also provides you with a guide of what sub-topics previous researchers may have missed, which you can then research yourself.