单项选择题

What is the advantage of the new air-conditioning system

A．The cost of the air-conditioning device is very low.
B．The working principle of the system is simple.
C．Minimal amount of energy is needed.
D．Only natural resources can be made use of.

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单项选择题

It can be inferred from the passage that on other planets

A．there is no oxygen for creating life
B．there is no suitable temperature for creating life
C．living things of different kinds may exist
D．living things similar to that on earth may exist

单项选择题

What are formed in the experiments in the first paragraph

A．Simple compounds of living things.
B．Simple matter named as amino acids.
C．Simple living organic molecules.
D．Simple dead organic molecules.