资料：Asked to name their favorite city, many Americans would select San Francisco which began as a small Spanish outpost located on a magnificent bay. The town was little more than a village serving ranchers when the United States took possession of it in 1846 during the war with Mexico.
San Francisco sprang into a city overnight because of the nearby discovery of gold in 1848.A great rush to California took place. Wagon trains plodded their dangerous way across 2000 miles of prairie and mountains, while hundreds of sailing vessels made the equally hazardous trip around the Horn. The vessels disgorged thousands of passengers -- then the crews deserted their ship and hundreds of vessels were left to rot in the bay. Within two years, California had enough population to become a state and San Francisco was for many years the hub of that newly-arrived population.
The city's present popularity is due to an excellent climate, an easy style of living ,good food, and numerous tourist attractions. The city is famous for its cable cars which "clang and bang" up the steep hills, and for its excellent seafood stalls along the wharf. Most visitors arriving from nations in the Pacific Basin spend several days getting to know the town.
In which year did California become an American state?（ ）
1850
本题考查的是细节理解。
【关键词】year; California; become an American state
【主题句】第2自然段 San Francisco sprang into a city overnight because of the nearby discovery of gold in 1848.Within two years,California had enough population to become a state and San Francisco was for many years the hub of that newly-arrived population.1848年，由于在其附近发现了金矿，旧金山一夜之间就变成了一座城市。在两年内，加州有足够的人口成为一个州，而旧金山多年来一直是新移民的中心。
【解析】本题的问题是“加州在哪一年成为美国的一个州？”。根据主题句可知，1848年在旧金山附近发现金矿。两年后，加州成为了一个州。因此，加州在1850年成为美国的一个州，故选A。
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