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

A．unavailable in rural areas.
B．shipped in refrigerator cars.
C．available in limited quantities.
D．a staple part of the American diet.

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.