In 1988, average global temperature increased to the highest recorded in the 20th century, causing increased concern about the effects humans are having on global warming.

A.to the highest recorded in the 20th century
B.to the level in the 20th century that was highest recorded
C.to the record high in 20th century
D.to a 20th century record high
E.to the highest level recorded in the 20th century