I don't know the options they gave you but here is some information that might help you.
Secondary sources are those that were created later by someone who didn't participate directly on the analyced events. For example, a diary of an U.S. soldier during WWII is a primary source. Later a historian writes a book analyzing the conditions of U.S. soldiers during that war, he uses the diary as primary source. The historian's book is a secondary source.
As you can see there are different inconveniences. First of all, the interpretation of the events has alredy been done by someone else, there can be misinterpretations, the information can be subjective. Using the same example iamgine the historian is a German soldier and wrote his book 5 years after the war. His research may be biased.
Another problem is that here might be a lot of infortmation to take in consideration. There are thousand of books, articles, internet sites, etc. that analyse the same subject. It is hard to decide wich one you are going to use.
Also, secondary sources can be just opinions without any scientific backround. It is important to check the profile of the authors to make sure they know what they're talking about.
One las thing to check is the year of the publication as it may be outdated, times change and something that could be correct in the past is now unacceptable.
I hope this helps you.