Bacteriophage is a virus that can "prey" bacteria. With the development of implantation technology in medicine, more and more patients are receiving medical implantation devices such as urinary catheters, heart stents, etc. There is a risk of bacterial infection, so some researchers believe that if the phage is adsorbed on the surface of the implant device material and placed in the patient, the infection caused by the implant device can be avoided. Which of the following is true. What weakened the conclusion above? ['For patients implanted with medical devices, antibiotics are generally used to prevent bacterial infections.', 'Where there are bacteria, there may be corresponding phages, but there are differences in the number.', 'Bacteriophages can attack pathogenic bacteria, but sometimes "prey" beneficial bacteria.', 'After some phages enter the body, they cannot adapt to the body fluid environment and it is difficult to maintain their activity.']