1. （2010·拉萨中学6次月考）While watching television, ____________.
A. the doorbell rang B. we heard the doorbell ring
C. there was someone knocking at the door D. we heard the doorbell rung
1B考查非谓语动词及状语从句的省略。根据watching television可知，主句的主语为“我们”，并且hear后接不带to的不定式作宾补。故选B。
2．（2010·北京西城二模）China is known greatly in terms of its cultural values over the past few years.
A．to change B．having changed C．changing D．to have changed
