Plant oils do not represent a new attempt to replace fossil fuels; it was already made by Rudolf Diesel in 1912.
HERE, THE ARE DOES NOT MAKE SENSE COMPLETELY. HENCE WE CAN ELIMINATE B,D.
(A) do not represent a new attempt to replace fossil fuels; it
THIS SENTENCE IS CORRECT AS REPRESENT IS PLACED CORRECTLY.
ANSWER A
(B) are not a new attempt to replace fossil fuels; the same one
HERE THE USAGE OF ARE IS INCORRECT.
(C) represent not a new attempt to replace fossil fuels, but one that
THE PLACEMENT OF REPRESENT IS NOT AS SOLID AS IN A.
(D) are not a new attempt to replace fossil fuels, but one that
HERE THE USAGE OF ARE IS NOT CORRECT. SAME AS BE
(E) are not new as an attempt to replace fossil fuels; it
THIS SENTENCE IS PARTIALLY CORRECT BUT A WOULD SOUND BETTER AND GRAMMATICALLY CORRECT.
ANSWER A