What is a common cause of peak tailing?
Simple answer to your question should be - None. Whoever designed this question for students does not understand the basic principles of analytical chromatography.
Under low concentration of analyte, which is the usual case, peak tailing has kinetic origins, or it could be from secondary interactions or due to the structure of the packed bed. All peaks in real chromatography tail to some extent i.e., none of them are 100% perfect Gaussians.
In rare cases, you can inject a lot of sample on an analytical column. There peak tailing  originates due to non-linear isotherms. This is what the test question is about. You have to read this section on isotherms Distribution Isotherms in Chromatography to choose the right answer.
There is another form of chromatography, called preparative mode, where you really inject a lot and this is where isotherms come in.