It can be inferred that railroad refrigerator cars came into use ______.

A．decreased in number
B．were on an irregular schedule
C．increased in cost
D．occurred only in the summer

A．Tin cans and iceboxes helped to make many foods more widely available.
B．Commercial ice factories were developed by railroad owners.
C．Most farmers in the United States raised only fruits and vegetables.
D．People who lived in cities demanded home delivery of foods.