31. According to the line chart, what is one trend in Taiwan's energy supply from 2004 to 2024?
(A) Energy generated by natural gas has gradually decreased for the last 20 years.
(B) Nuclear energy has accounted for more than 10% of the energy supply since 2004.
(C) Coal and coal products have been supplying about 30% of the total energy since 2004.
(D) Energy supplied by oil and petroleum products has steadily increased over the past 20 years.