题目

 Though famous all over the world, Yuan Longping, sunburnt, ______ with his simple life and ____ in plain clothes, is still busy with his experiment to improve his super-hybrid rice.  A. being satisfied; being dressed   B. satisfying; dressing  C. satisfied; dressed     D. to be satisfied; to be dressed 答案：C下列气体中，可以用向上排空气法收集的一组气体是A．O2、CH4B．CO2、CH4C．NH3、H2D．CO2、O2