They heard a message from a spacecraft.（用just改现在完成时） They ___ just ___ a message from a s

They heard a message from a spacecraft.（用just改现在完成时） They ___ just ___ a message from a s
They heard a message from a spacecraft.（用just改现在完成时）
They ___ just ___ a message from a spacecraft.
Have you got a letter from Lucy?（改同义句）
Have you ____ ____ Lucy?
To understand the problem is very difficult.（用it作形式主语）
_____ _____ very difficult ____ understand the problem.
I came here two days ago.（改同义句）
I ____ ____ here _____ two days.
Her mother has been to HongKong (seveal times).（对括号提问）
_____ _____ _____ has her mother been to HongKong?