When conducting research, all of the following are ways to find quality sources, except looking through trade journals. searching the internet. using outdated reference books. asking experts on the subject.

Using outdated reference books

Depending on what is being researched, outdated reference books are not quality sources. They often contain information that is incomplete or information that was gathered before certain advances in science have revealed new data. Trade journals are written by experts in a specific field so these are often reliable sources. Also experts on the subject would be considered a perfect primary source. Lastly, the internet is acceptable for finding quality sources so long as the researcher is careful about which websites are used for the research.

the answer is "began" because it is a action that can be done