搜题请搜索小程序“爱下问搜题”
问题 单项选择题

当渐缩喷管出口的外界压力为绝对真空时(绝对真空的比热容为∞)，则质量流量( )。

A．等于0
B．等于临界流量
C．大于临界流量
D．介于零和临界流量之间

答案

参考答案：B

单项选择题

Because the process of freezing food consumes energy, many people keep their electric freezers half-empty, using them only to store commercially frozen foods. Yet freezers that are half-empty often consume more energy than they would if they were kept fully stocked.
Which of the following, if true, contributes most to an explanation of the apparent discrepancy described above ？（）

A．A given volume of air in a freezer requires much more energy to be maintained at a temperature below freezing than does an identical volume of frozen food.

B．The more often a freezer’s door is opened, the more energy is required to maintain that freezer’s normal temperature.

C．When unfrozen foods are placed in a freezer, the average temperature of a given volume of air inside that freezer rises temporarily.

D．A person who normally maintains a half-empty freezer can cut energy costs considerably by using a freezer that is 50 percent smaller.

E．An electric freezer can operate efficiently only if chilled air is free to circulate within the freezing compartment.
查看答案
单项选择题

以下哪项业务是中国户口管理的特有业务（）

A.编写住房门牌

B.身份证件管理

C.住户人口档案资料管理

D.重点人口管理
查看答案