题目内容：
根据下面内容，回答题： We show an amazing tolerance for a form of pollution that is a growing problem: noise. Airplane traffic is increasing by five percent a year. Urban noise is doubling every ten years. By air, land and sea, we are facing an onslaught of noise that is threatening our ability to live in this world.
We have granted ourselves the right to make noise. But what about our responsibilities? Have we developed a sense of acoustic responsibility?
The evidence suggests that we have not. Many people seem to believe they have an unlimited right to make noise with cars and motorbikes, and with loud music at home and in the street. In some countries measures have been taken to force people to make less noise. In Britain, for example, a law has been passed preventing people from disturbing their neighbors with music at night.
It is widely accepted that we should deal with our rubbish in a responsible way. Noise is in reality a particularly insidious (潜在的) form ofrubbish. It destroys community life, pursues us into our homes, keeps us from sleeping and is the cause of many stress-related illnesses, as well as hearing loss.
Our acoustic environment belongs to all of us. Everyone has the right to use it, but no one has the right to abuse it. Let's start using it responsibly.
The level of noise produced in cities and towns________. A．is four times higher every ten years
B．is four times lower every two years
C．is twice as high now than ten years ago
D．is twice as high now than two years ago
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