锁、眼镜、羽毛，最重的是____，最轻的是____。

根据对话内容，将方框内符合对话情境的句子抄写在对话空白处，使对话恢复完整，选项中有两项是多余的。

（An interviewer is interviewing a Chinese student who is studying in America.)

A=an interviewer       B=a Chinese student

A: Excuse me,   ____     

A: How long have you been studying here?

B: ____      

A: How are you getting on with your study?

B: Very well.

A:  ____                    

B: I'm going back to China.

A: Why?

B: Er, you know,China is developing faster and faster.  ____ 

A: Any more reasons?

B: Yes, I'd like to spend more time with my parents.

A: Wow! Good! Caring for parents comes first in China.  ____ 

B: Thank you.

三个质数的最小公倍数是42，这三个质数是____。