小题1:It is about 5500 miles long.
小题2:The ancient Chinese began to build some walls around 600B.C.
小题3:Qin Shihuang, the first emperor of China, joined the old walls together.
小题4:Yes, they do.
小题5:Because some sections of it are falling down.
小题1:It is about 5500 miles long.
小题2:The ancient Chinese began to build some walls around 600B.C.
小题3:Qin Shihuang, the first emperor of China, joined the old walls together.
小题4:Yes, they do.
小题5:Because some sections of it are falling down.