Trả lời bởi giáo viên
Đáp án đúng: c
$\overset{+4}{\mathop{C}}\,{{\overset{-2}{\mathop{O}}\,}_{2}},\text{ }{{\overset{+1}{\mathop{H}}\,}_{2}}\overset{+4}{\mathop{C}}\,{{\overset{-2}{\mathop{O}}\,}_{3}},\text{ }\overset{+1}{\mathop{H}}\,\overset{+2}{\mathop{C}}\,\overset{-2}{\mathop{O}}\,\overset{-2}{\mathop{O}}\,\overset{+1}{\mathop{H}}\,,\text{ }\overset{-4}{\mathop{C}}\,{{\overset{+1}{\mathop{H}}\,}_{4}}$
