参与细胞分裂的、由微管组成的结构有（） A.缢缩环 B.染色体 C.中心粒 D.纺锤

Which of the following call be inferred from the passage about cotton production in the United States after the introduction of Whitney's cotton gin

A．( More cotton came from sea island cotton plants than befor

B．( More cotton came from short-staple cotton plants than befor

C．( Most cotton produced was sold domesticall

D．( Most cotton produced was exported to Englan

虚仓入库单只能手工录入。（）

广防己横切面中心部有异型复合维管束，其韧皮部位于内方。（）

在设置防火墙确有困难的场所，可采用防火卷帘作防火分隔，当采用包括背火面温升作为耐火极限判定条件的防火卷帘时，其耐火极限不低于（）。

A．3.00h

B．2.50h

C．2.00h

D．1.00h

固溶体