What are you looking for in your observation when you're looking for evidence and reaction

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?

How can a geological time scale best be reconstructed? a) comparing vestigial structures in living species b) comparing homologous structures in living species c) examining homologous structures in fossil remains d) examining the written records of scientists from past cultures

According to this food web which of the following would be considered primary consumers