s Beidou global satellite navigation system willhave been completed by 2020, ____ of more than 30 satellites

Nobody knows for sure what effect the global warming have ______ our environment in the long term

by a greater demand forvegetables,farmers have built more green houses.

He sometimes ___________ a train to work.

How about joining us in the summer camp —I wish I could, ___________ I have to practice forthe piano test.