The graph illustrates the primary sources of 
energy
 in Use synonyms
USA
 from 1980 to 1990
Correct article usage
the USA
Overall
, it is noticeable that the oil had the highest percentage of Linking Words
energy
 in Use synonyms
both
 Use synonyms
years
, Use synonyms
while
the proportion of hydroelectric Linking Words
power
 Use synonyms
had
 the lowest. Verb problem
was
Moreover
, the percentage of coal and nuclear Linking Words
power
 increased in Use synonyms
both
 Use synonyms
years
, except Use synonyms
natural
 gas and oil.
Change preposition
for natural
To begin
 with an oil, it accounted for 42 % in 1980 which decreased in 1990. Linking Words
However
, it was the
highest sources of Linking Words
energy
 in Use synonyms
both
 Use synonyms
years
. The figure for natural gas  obtained , namely 26 % which Use synonyms
was 
dropped to 1 % in 1990 (25).  Unnecessary verb
apply
However
, the proportion of coal Linking Words
had
 Verb problem
was
the 
22% which  rose gradually  to 27% in 1990.
With regards to hydroelectric Correct article usage
apply
power
, it accounted for 5 % and maintained the same level in Use synonyms
both
 Use synonyms
years
. Use synonyms
However
, it was the lowest source of Linking Words
energy
 over the period in question. Use synonyms
Furthermore
, the percentage of nuclear Linking Words
power
 showed Use synonyms
significant
 increase, which became twice bigger compared to 1980 (10%)Add an article
a significant