The pen ________ he is writing is mine.

They returned home after a long journey, _______. [ ]

We usually do some cleaning _____ weekends.

Green economy offers a new model ________ people could both protect the climate and develop the economy, according to what Li said at the International Cooperative Conference on Green Economy and Climate Change

Yunnan province in China was attacked by such a terrible drought this early spring ____________few people had experienced before, ____________ made us worry about global climate changes