11.I don't think _____possible to master a foreign language without much memory work.
A.this B. that C. its D. it
11.D【解析】it是形式宾语，to master…是真正宾语。此句还可说成I don't think it is possible to…。
12.______of them knew about the plan because it was kept in a secret.
A.Each B. Any C. No one D. None
13. He paid the boy ￥10 for washing ten windows，most of _____hadn't been cleaned for at least a year.
A.these B. those C. that D. which
14.Kate and her sister went to holiday with a cousin of _____.
A.their B. theirs C. her D. hers
15.I invited Tom and Ann to dinner，but _____of them came.
A.neither B. both C. either D. none