However, quality is more important that quantity. Photos, charts, and graphs often express things better than a whole paragraph, and are welcome as well. In scientific writing, text should be void of superfluous verbiage, and wording should be clear and unambiguous. Any data or ideas derived from one of your sources must naturally be cited. The selection of these sources must be made critically.
Some sources are biased rather than objective.
Peer-reviewed publications make the best references. Most of the time, a paper can be written with 5-10 of these sources, listed in a separate section at the back. The style to be used for citations is not critical, but be consistent for all of them. The oral presentation of your theme paper should be 8-12 minutes. Follow a format similar to that in the written report.