Depression is a serious problem for residents of nursing homes. However, a recent study has found that residents who developed personal bonds with pets had significantly lower rates of depression than did residents who did not develop personal bonds with pets. Which one of the following statements is most strongly supported by the information above? ['The best method for helping a nursing-home resident to overcome depression is to provide access to a pet.', 'High rates of depression among nursing-home residents may result at least in part from a lack of companionship.', 'Allowing free access to pets in nursing homes would eliminate problems relating to depression.', 'Animal companionship is essential for psychological well-being.']