In the environment area, there is a system （ ） the waste is disposed of by using the principles of ecology.
A.正确答案Ain which
B.which
C.on which
D.that
In the environment area, there is a system （ ） the waste is disposed of by using the principles of ecology.
In the environment area, there is a system （ ） the waste is disposed of by using the principles of ecology.
A.正确答案Ain which
B.which
C.on which
D.that
