I dont think ________ possible to master a foreign language with

I dont think ________ possible to master a foreign language without much memory work.
A、it
B、that
C、this
D、those
【正确答案】：A
【题目解析】：think it to be adj that 认为 ……是……的；it 做形式宾语，指代 that 从句 的内容