题干
He went from door to door, _______ waste papers and magazines.
A：gathering
B：gathered
C：gather
D：being gathered
答案(点此获取答案解析）
A
A：gathering
B：gathered
C：gather
D：being gathered
Fe3O4+6HCl↑+H2↑
6FeCl3+6H2O+O2
2FeCl2+Cl2↑