Carla, curious as to the cause of disease in her mother's plants, designed the following experiment. She crushed the infected leaves with sterile water. Then, the solution was filtered once through a funnel filter and once through a 0.4 micron filter. Both the filtrate and residue of each filter were kept and tested by rubbing each, individually, onto uninfected plant. The table below shows the result:

                                                                          Infection                               No infection

Funnel filtrate                                                         X                                 

Funnel residue                                                        X

Second filtrate                                                                                                         X

Second residue                                                       X

Which one of the following is the most likely pathogen? (choose all correct answers)

a) virus

b) bacteriophage

c) bacterium

d) fungus

e) none of the above