单项选择题

What does the passage mainly discuss

A．The production of solar light and heat.
B．The physical and chemical nature of life.
C．The conversion of Hydrogen to helium.
D．Radiation in the X - ray part of the spectrum.

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单项选择题

It can be inferred from the passage that the Sun’s light travels ______.

A．through solid objects in space
B．in many different directions
C．more slowly than scientists previously believed
D．further in summer than in winter

单项选择题

The main purpose of the passage is to ______.

A．compare skyscrapers with other modern structures
B．describe skyscrapers and their effect on the environment
C．advocate the use of masonry in the construction of skyscrapers
D．illustrate some architectural designs of skyscrapers