In 1900, the energy derived from burning petroleum was only four percent( ) of coal.
A.正确答案Athat
B.this
C.what
D.which
In 1900, the energy derived from burning petroleum was only four percent( ) of coal.
In 1900, the energy derived from burning petroleum was only four percent( ) of coal.
A.正确答案Athat
B.this
C.what
D.which