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  3. We’ve all used thermometers to measure temperature butsometimes we need to

We’ve all used thermometers to measure temperature butsometimes we need to

游客2023-09-13  62
问题     We’ve all used thermometers to measure temperature but
sometimes we need to measure temperature in places you can’t put           【S1】______
a thermometer — for example, inside a rocket engine. One of the
best methods for those really hard-to-get-to place is based on laser       【S2】______
spectroscopy. Light from a laser pointing at the region of interest        【S3】______
is absorbed by molecules and some of it are re-emitted back                【S4】______
towards the source where it can be measured. The re-emitted light
is shifted in frequency (changed in wavelength) by amounts that
depend on the molecule and also the temperature and pressure of            【S5】______
the surrounding gas because of collisions among the molecules.
The single, sharp frequency from the laser is thus smeared out in
to a whole spectrum of frequency whose shape can be used to                【S6】______
determine the temperature provided so that the molecular
transitions and line shapes are known.  Because it ’is the main           【S7】______
component of the air, it is convenient to use nitrogen since its
molecular properties are known from room temperature to                    【S8】______
temperature of about 1,200 degree Celsius from experimental
measurements. Although this is a large range, it is far short of           【S9】______
what it is needed for some applications.                                   【S10】______ [br] 【S3】
选项
答案 pointing→pointed
解析 由于激光是被动指向目标，应该用过去分词。
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