中国完全陷入半殖民地半封建社会境地的标志是 A．《马关条约》签订 B．袁世凯窃取

植物的果实和种子分别是由什么结构发育而来的（　　）

A．子房壁、胚珠

B．子房、胚珠

C．子房壁、受精卵

D．子房、受精卵

下列物质对应的化学式不正确的是

A．氧化镁-MgO

B．石灰水-Ca(OH)₂

C．氧气-O

D．氧化铜-CuO

根据肿瘤在肺内的发生部位，肺癌肉眼类型可分为（）

A.表浅型和浸润型

B.巨块型、多结节型和弥漫型

C.特发型和家族型

D.中央型、周围型和弥漫型

E.息肉型、菜花型和深部浸润型

With respect to determining the optimal portfolio for an investor, which of the following statements is most accurate（）

A. Two investors may choose the same optimal portfolio even if their indifferent curve are different.

B. Less risk-averse investors will have steeper utility curves than more riskaverse investors.

C. The optimal portfolio lies at the point of tangency between the efficient frontier and indifference curve with the highest possible utility.

混凝土搅拌时间是指从全部原料投入到出料为止的时间。( )