25.A.self-satisfaction B. self-protection C. self-respect
D. self-service
)
Why
is a space left between the rails of a railway line where one piece joins the
next? The space 1 to let the rail expand (膨胀)when it gets 2 . On a hot day, the metal
expands and if it 3 to do this, the rails would bend 4 shape. This caused railway 5 in the past.
6 solids expand much less
than liquids or gases, the 7 increases (增加量) can add up to a lot, when there
are long 8 of
rail. For example, the difference in length of rail, in summer and winter, 9 the distance between London
and Edinburgh,
is about 1/4 mile.
We 10 keep in our minds and must not
forget the expansion of metal when we build a very long metal bridge 11 . So spaces are left in the
places 12 the metal is joined.
When 13 colder, it becomes smaller in
size. We can make use of the
14 that solids expand
when they are heated, and become smaller in size when they get colder, and 15 they do it at different 16 .
For
example, when an iron band (铁箍) has to fit tightly
17 a wooden wheel, first we
make it 18 than the wheel, then we 19
it, so that it goes on easily. When it gets colder, it becomes smaller
in size and 20 the wheel very tightly.
