北大2013年考博士英語真題及答案

北大2013年考博士英語真題及答案
Part Two: Structure and Written Expression20
Directions: In each question decide which of four choices given will most suitably complete the sentence if inserted at the place marked. Mark your choices on the ANSWERSHEET.
21.The nuclear family __________ a self-contained, self-satisfying unit composed of father, mother and children.
A. refers to　B. defines　C. describes　D. devotes to
22.Some polls show that roughly two-thirds of the general public believe that elderly Americans are________ by social isolation and loneliness.