Such is         human nature that many people don’t value         things they possess until they’ve lost them .

A．不填；不填

B．不填;the

C．the; 不填

D．a; the

属于极性溶剂的是

A．甘油
B．聚乙二醇
C．丙二醇
D．液状石蜡
E．乙酸乙酯