单项选择题

XYY个体细胞中，Y染色质的数目是

A．2
B．1
C．3
D．0

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单项选择题

At some point after modern humans entered Europe and Asia, the Neanderthals vanished from Earth. The reason for their disappearance remains a mystery. There are, however, a number of theories. As modern Homo sapiens _____________ their lands, they may have killed the Neanderthals off. Other possible causes include diseases introduced by the newcomers, or climate change.
A、scattered
B、traced
C、conquered
D、proofed

单项选择题

有毒物质‘“龙葵素” 在绿皮马铃薯和() 马铃薯中存在，食后会中毒

A．黄皮
B．红皮
C．发芽
D．白皮