【单选题】Which of the following is a feature of a democracy?
A.
Exercise of absolute control by one person or political party.
B.
Governance by people or elected representatives.
C.
Prohibition of entry to opposing political parties.
D.
Complete restriction of individual political freedom.
【判断题】1608销售包装,又称为大包装,内包装或者直接包装。
【单选题】which feature of a centrifugal pump reduces the need for renewing worn impellers and pump casings?
A.
close radial clearance between impeller hub and casing.
B.
Low rotational speed of impeller.
D.
Replaceable impeller and casing wear rings.
【单选题】听力原文:There's no doubt that athletes are playing hard enough to suppress immune defenses. The normal population in Australia expects to get between three and four upper respiratory infections each year...
【简答题】麦植物学家约翰生通过对商用菜豆品种进行连续选择⇒分离出19个纯系⇒提出()约翰生认为商用菜豆是多个纯系的混合体,在该混合体内选择有效,但仅能分离出不同纯系,若继续在纯系内进行选择无效。纯系学说试图阐明两个问题:①选择作用只是隔离变异⇒认为达尔文的选择学说不能说明生物进化的动力问题;②环境条件引起的变异不能遗传⇒认为拉马克提出的获得性状遗传也无根据。