Which of the following best states the central idea of the passage?
A. China's rail and metro systems have experienced rapid growth from backwardness, and today they greatly help to relieve the pressure of an increasingly large number of travelers due to the rapid economic growth.
B. China's rail and metro systems have experienced rapid growth from backwardness, and today, they boast the highly sophisticated computerized services and the world's most extensive high-speed rail network.
China's rail and metro systems have experienced rapid growth from backwardness, and today they are playing a vital role in the new period of the great rejuvenation of the Chinese nation.
D. China's rail and metro systems have experienced rapid growth from backwardness, and today they serve as the foundation of the continual development within our national transportation sector.
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