[单项选择]

The use of heat pumps has’ been held back largely by skepticism about advertisers’ claims that heat pumps can provide as many as units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation. Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body or air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from th
A. explain the differences in the working of a heat pump when the outdoor temperature changes
B. contrast the heating and the cooling modes of heat pumps
C. describe heat pumps, their use, and factors affecting their use
D. advocate the more widespread use of heat pumps

[单项选择] The use of heat pumps has been held back largely by skepticism about advertisers’ claims that heat pumps can provide as many as units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation. Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body of air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from the air to the
A. explain the differences in the working of a heat pump when the outdoor temperature changes
B. contrast the heating and the cooling modes of heat pumps
C. describe heat pumps, their use, and factors affecting their use
D. advocate the more widespread use of heat pumps

[单项选择]

The use of heat pumps has’ been held back largely by skepticism about advertisers’ claims that heat pumps can provide as many as units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation. Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body or air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from th
A. heating is least essential
B. electricity rates are lowest
C. its compressor runs the fastest
D. outdoor temperatures hold steady

[单项选择]We find that bright children are rarely held back by mixed-ability teaching. On the contrary, both their knowledge and experience are enriched. It is rather unreal to grade people just according to their intellectual ability without taking into account the fact that children develop at different rates. It can be quite discouraging to be at the bottom of the top grade to children!
Besides, we are concerned to develop the abilities of all our pupils to the full, not just their learning ability. We also emphasize personal qualities and social skills, and we find that mixed-ability teaching is important to all these aspects of learning.
In our classrooms, we work in various ways. Working in groups, the pupils get the opportunity to learn to cooperate, to share, and to develop leadership skills. They also learn how to cope with personal problems as well as learning how to think, to make decisions, to analyze and evaluate, and to communicate effectively. The pupils learn from e
A. argue for teaching bright and not-so-bright pupils in the same class
B. recommend pair work and group work for classroom activities
C. offer advice on the proper use of the library
D. emphasize the importance of appropriate formal classroom teaching