The Foley bag must be kept lower than the patient's bladder so that.. urine will not return to the bladder, causing infection

The Foley bag must be kept lower than the patient's bladder so that:
a. urine will not leak out, soiling the bed
b. urine will not return to the bladder, causing infection
c. the bag will be hidden and the patient will not be embarrassed
d. the patient will be more comfortable in bed

Answer b.
 Raising the bag above the bladder level can lead to backflow of the urine, with its bacteria, into the bladder.