The supply of oil can be shut off unexpectedly at any time, and in any case, the oil wells will all run dry in thrty years or so at the present rate of use.
石油供应可能会随时意外中断；不管怎样，以目前这种消费速度，只需30年左右，所有的油井都会枯竭。
2
Dividing the reads by the read requests gives the miss rate — in this case, 0.6 misses per 1,000 requests.