I remembered having locked the door, but I came back to .
People are advised not to smoke at home, since passive smoking is ________ topeople around them. Which is Not proper for the blank?
He stumbled(绊倒)on the _______ ground and fell flat on his face.
Many students today suffer from ________ problems, since they are under too much pressure.
________ energy is generated from natural resources—such as sunlight, wind, rain, tides and so on.
Effective measures have been taken to prevent _______pollution.