肝片吸虫的发育史过程为（） A.虫卵→毛蚴→尾蚴→成虫 B.虫卵→毛蚴→毛虫蚴→成虫

     The trip to that city was eye opening for everyone,and near its end,all the young people
in our group began to reflect on what it had meant.We   1   the first night we had arrived.
We had all gone into the markets of the city   2   the young people could experience its
energy.But what we actually saw simply   3  us all-the rundown houses,the children in rags,
the people begging for money...Walking home,  4   under a low bridge,we came across   5  
families of homeless people seeking a bit of dry ground to sleep on   6   the night.We had to
step over bodies as we found our way through the darkness.
     The poverty (贫困) was  7   than anything my young companions had ever imagined.Back
in the hotel,an air of sadness settled over the group.Many  8   and cried.Spending time in this
  9   moves a person to care about humanity.
     That evening,our group spent hours talking about what we had   10  .Gently,I encouraged
everyone to talk about the difficult   11   that day's discoveries had inspired. Sitting together
   12   a circle as everyone had a chance to speak,we all began to realize that   13   of us was
alone in our struggle to cope with our reactions.
     Based on my   14   in poverty stricken areas,I suggested that   15   the emotions we had
were painful,they could also be important in helping us to move forward.We all   16   that we
had seen things that should never be allowed to happen.  17  ,what could we do about it?
Together,we began to brainstorm ways we could help to ease the   18   we had seen.As I
encouraged group members to focus on   19   they could do,a sense of determination   20  
the previous sadness.Instead of despair,these young people began to feel a call to action.