剖切符号的转折处不允许与轮廓线重合。（ ）
A. 对
B. 错
Cotton became the most profitable crop in the South mainly because of the——
A. use of irrigation on plantation
B. Whitney’s cotton gin
C. slave labour
D. improved agricultural techniques
Gold was discovered in California in ——————
A. 1828
B. 1838
C. 1848
D. 1858
The first transcontinental railroad in the US was completed in————
A. 1850
B. 1859
C. 1869
D. 1890
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