In 1848 a settler in distant, undeveloped California discovered gold near Sacramento. As the news spread, a great tide of gold-hungry men flowed into California. They came from all parts of the United States in tens of thousands. There were even gold-seekers from Europe. Some of the people move across the country by cart, traveling almost half a year and meeting many hardships and dangers. Other sailed all the way around South Africa, finally reached the California shore. Since the first discovery was of tiny pieces of gold at the bottom of a stream, many of them searched the waters of rivers for the precious bits of yellow metal. Others made channels to draw off flowing water in order to examine it carefully for bits of gold. They worked with almost full determination and fierce competition(竞争). Life was hard and rough in the days of the California gold rush. A few of the adventurers became rich, but most of them were bitterly disappointed. After having removed from their homes and after traveling the long, dangerous road to California, they had found little or nothing. Some returned home. But many remained in California to work and to settle as ordinary citizens without the riches they had dreamed of. It was this great arrival of population that built up California very fast and led to its becoming a state of the United States in 1850. Many people rushed to California because

A. they were hungry for discoveries
B. they were attracted by gold
C. they wanted to build up California
D. they looked for a new competition