the boy was walking down the street when the UFO landed改为一般疑问句,并回答while the boy was walking down the down the street ,the UFO landed（改为一般疑问句,并回答）the girl was shopping when the alien got out（改否定句）while the girl was shopping ,the alien got out（改否定句）

the boy was walking down the street when the UFO landed改为一般疑问句,并回答
while the boy was walking down the down the street ,the UFO landed（改为一般疑问句,并回答）
the girl was shopping when the alien got out（改否定句）
while the girl was shopping ,the alien got out（改否定句）