下面是几个同学关于理想的议论，你认为正确的是

①理想理想，有利才想  

②理想等于空想，是要把握好现在 

③明确目标，树立理想，是保证我们取得成功的第一步  

④有理想，人生才更有意义

A、①②③④    

B、①②③      

C、①②④       

D、③④

At the beginning of class, the noise of desks____________ could be heard outside the

classroom.                    [ ]

A．opened and closed

B. to be opened and closed

C. being opened and closed

D．to open and close