单项选择题

听力原文： Piglets may be happy wallowing in the mud, but they get a much better start in life if they are nurtured on a warm waterbed. Instead of snuggling up to their mothers for warmth in their cold pigsty and running the risk of being crushed--a common cause of early death--German scientists said waterbeds could be a safer alternative.
When Martin Ziron and researchers at the Institute of Animal Breeding and Genetics in Giessen, Germany tested various heating methods on 1,400 piglets during their first weeks of life, waterbeds won hands down.
'Around 99 percent of the piglets preferred warm waterbeds to any of the alternatives, spending well over half the day lounging about on them and only getting up to feed or play,' New Scientist said Wednesday.
The scientists compared the number of injures, which usually occur while scrambling for a feeding position, and the weight gain of the piglets which were provided with plastic plates, foam mats waterbeds, straw or concrete. Piglets on the waterbeds had fewer injuries and gained much more weight than the animals kept on concrete.
According to the magazine, the waterbeds are made from a tough plastic membrane and can be heated from underneath by an electric mat or from above by infrared lamps.
From the passage we know that piglets
A．easily get crushed in the first weeks
B．does not like warm waterbeds in the beginning
C．generally like snuggling up to their mothers for warmth
D．are not happy wallowing in the mud