In the 6th sentence of the 2nd paragraph, the word "This" refers to______.
A) the decrease of the oil industry C) the government’s assumption
B) the increase of measures taken D) the level of sulphur dioxide

A．In the 6th sentence of the 2nd paragraph, the word "This" refers to______.
B．the decrease of the oil industry
C．the increase of measures taken
D．the government’s assumption
E．the level of sulphur dioxide