A:﹣2<k<2
B:﹣2<k<0
C:0<k<4
D:0<k<2
①加入A时生成白色沉淀;
②往①沉淀中加入B时沉淀溶解,并有气体逸出;
③往②生成的溶液中加入C时,又有白色沉淀生成.
根据上述现象,回答:
The Red Army soldiers had to fight ________ all kinds of difficulties in their fight ________ the people's freedom.