Transit, a car made in Jiangxi province, was sold nearly 50,000 units in 2012, with the total value_____ it was in 2008．

A．more than three times what

B．three more times than that

C．over three times than what

D．over three times of that

高温或猛烈撞击均会使化肥硝酸铵发生剧烈的分解反应，生成大量气体，放出大量的热，因而发生爆炸。已知硝酸铵爆炸反应化学方程式为：2NH₄NO₃==2N₂↑+O₂↑+4X，则X的化学式是________。