单项选择题
A.It has a dense population. B.It has many towering buildings. C.There are 200 vehicles for every kilometer of roadway. D.There are many museums and palaces.
A.They could drive the insects away. B.They could keep the plants well watered. C.They could build devices to trap insects. D.They could make the plants grow faster.
A.For education. B.For adventure. C.To enjoy themselves. D.To look for a different lifestyle.