皮皮学，免费搜题
登录
搜题
【简答题】
It’s necessary for her to change her dress after a busy day. She needed __ her dress after a busy day.
拍照语音搜题，微信中搜索"皮皮学"使用
参考答案：
参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】Subjects are said to be assigned randomly when
A.
they are assigned to experimental and control groups from a sample which is representative of the larger population.
B.
they each have an equal chance of being assigned to either the experimental or control group.
C.
they are assigned to experimental and control groups so that the groups differ on some critical variable before the experiment begins.
D.
neither the experimenter nor the subject knows whether the subject is in the experimental or control group.
【简答题】液压泵是一种将机械能转换为液压能的能量转换装置。它为液压系统提供具有一定压力和流量的液体,是液压系统的一个重要组成部分。 构成液压泵的基本条件是什么?
【简答题】构成液压泵的基本条件是：