在中国，自行车是最为流行的交通工具。
2．骑自行车有许多好处。
3．自行车的未来……

A. what should study
B. what be studied
C. what to study
D. what studied

A. the upper-upper class is of aristocratic origin
B. the "old rich" enjoy higher prestige than the "new rich"
C. the "old rich" isolate themselves and lead a lonely life
D. the upper class owns at least a quarter of the country’s wealth