27. ______ days went by, the tree grew taller and taller.
    
        
            | A. As | B. As soon as | C. When | D. After | 
    
 
28. One of the best ways for people to keep healthy is to ______ good eating habits.
    
        
            | A. grow | B. find | C. increase | D. develop | 
    
 
29. They arrived ______ Shanghai ______ a cold morning.
    
        
            | A. in, in | B. in, on | C. at, on | D. at, in | 
    
 
30. He ______100 dollars ______ a plastic cup. It was too expensive.
   A. spends, on      B. spent, in         C. spent, on        D. spends, in