The engineers must have worked out the design by the end of last week，_______？

The volunteers try to convince people _____the fact that some species are in danger of _____.

I must find out why＿＿＿＿so many students made the same mistake.

ain ___________ obvious the moment Iwalked into the room, for the first man I met asked me pitifully:"Are you feeling all right"

Do you know _______ the Capital Museum—Next Friday.