4．
虽然中国移民在淘金热时期就开始到来了，但是更大批量的移民却是在1 9世纪60年代为了修建贯穿美国东西海岸的铁路而来的。
Although Chinese immigrants began to arrive during the Gold Rush Period, it was the ____________of the rail network from the west to the east coast_________ brought even larger numbers to California in the 1860s.