Based on the figure below, which of the following statements is/are a direct reflection of the data presented? (select all that apply.)

a. increasing ivory prices always increases the amount of illegal killing of elephants.
b. natural mortality rate is higher than the illegal killing rate of elephants between 1998 and 2006.
c. in 2010 illegal killing rates surpassed natural mortality rates of elephants.
d. after 2008, increasing ivory prices are associated with increases in illegal killing of elephants.