[听力原文]11-15
People are living longer and longer. As a result, more and more middle-aged adults have to take care of their ageing parents. When your parents can no longer care for themselves, these adults may be forced to stay at home to care for them. Taking care of ageing parents is quite difficult. For example, an ageing parent may become blind. He or she needs children to perform a lot of everyday work. The roles of parents and children are then changed. Children are forced to care for their parents as if their parents were children. When children find it difficult to take care of their dependent parents, they often decide to take them to a nursing home. There, proper care and attention can be given. This allows the children to return to their normal everyday life.
有关亚慢性毒性试验的目的，不正确的是（）
Until recently, mobile radio was to wireless communications what the Yugo was to transportation. With a mixed clientele ranging from truckers using CBs to police armed with walkie-talkies to taxi drivers dispatched by radio, it was viewed as an unglamorous business and a technological backwater.
But specialized mobile radio, as it is known, has been rediscovered. It is now considered one of the biggest prizes in the all-out war for the public airwaves. The reason: high-tech companies have figured out how to profitably rebuild the antiquated dispatching system into an advanced cellular-telephone network that can take on the likes of AT & T and the giant Baby Bells. Upstart Nextel Communications sent shock waves through the industry last week when it agreed to buy Motorola’s SMR frequencies for $1.8 billion.
That could pose a serious threat to cellular hegemony. Although both systems are based on the same basic technology, SMR systems are digital and cover
A. Its technological features have radically changed
B. It has been rebuilt to cater to various subscribers
C. Its dimensions have been reduced by wide margins
D. It was connected to a greater variety of services
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