题目根据"绿色化学"的理念,某化学家设计了下列化学反应步骤:①CaBr2+H2O 750℃ ‾CaO+2HBrCaBr_{2}+H_{2}O\frac{\underline{\;750℃\;}}{}CaO+2HBrCaBr2+H2O750℃CaO+2HBr②2HBr+Hg 100℃ ‾HgBr2+H2↑2HBr+Hg\frac{\underline{\;100℃\;}}{}HgBr_{2}+H_{2}\uparrow2HBr+Hg100℃HgBr2+H2↑③HgBr2+CaO 750℃ ‾HgO+CaBr2HgBr_{2}+CaO\frac{\underline{\;750℃\;}}{}HgO+CaBr_{2}HgBr2+CaO750℃HgO+CaBr2④2HgO 500℃ ‾2Hg+O2↑2HgO\frac{\underline{\;500℃\;}}{}2Hg+O_{2}\uparrow2HgO500℃2Hg+O2↑则该方案主要目的是为了制备（ ）A.HgBr2HgBr_{2}HgBr2B.CaOCaOCaOC.H2H_{2}H2D.HgHgHg知识点：化学的用途章节：专题1 化学造福人类 / 单元1 造福人类的化学
