以2、-3为根的一元二次方程是（        ）

如图，在平行四边形ABCD中，E为CD上一点，连接AE、BE、BD，且AE、BD交于点F，S_△DEF：S_△EBF：S_△ABF=9：21：49，则DE：EC=（　　）

   Mrs.  Wilson is my neighbor(邻居). She    1  at a post office and she meets lots of people   2  . She is    3  to everyone and likes helping others. She is over fifty years old,   4   she looks very young(年轻). She is of  5 height and thin. She has long,  curly,  brown   6  . She likes to wear a red T-shirt and jeans. She  7  like a movie star. She really likes 8 shopping on weekends and she always buys many beautiful clothes. She always 9  , “Old people still want 10  beautiful! ”People all like her very much.

下列哪一项措施能提高森林生态系统的稳定性（　　）