The pie charts compare the contribution of different means for producing electric energy in the US in 1980 and 1990. 
As is illustrated in both charts, 
although
 oil contribution fell from 42 per cent in 1980 to 33 Linking Words
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percent
 in 1990, it still comprises the most significant share of electric Change the spelling
per cent
power
 generation in both of the pie charts.
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Besides
 oil, natural gases, and coal had the second and third proportion for Linking Words
power
 generation in 1980 with 26 and 22 Use synonyms
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percent
 in turn. The percentage of these two mentioned electricity production methods had changed slightly in 1990, Change the spelling
per cent
however
, these minimal changes reversed their position to the coals becoming the second most used method for Linking Words
power
 input in 1990 with 27 Use synonyms
Use synonyms
percent
 share and natural gas reaching 25 Change the spelling
per cent
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percent
.
Meanwhile, hydroelectric Change the spelling
per cent
power
 remained exactly the same in both figures with 5 Use synonyms
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percent
 proportion of the whole Change the spelling
per cent
while
 the share of nuclear Linking Words
power
 doubled from 5% in 1980  to 10% in 1990.Use synonyms