________ you happen to see Mary, would you please ask her to come here?
After Yang Liwei succeeded in circling the earth, Chinese astronauts __________ walk in space.
Students are encouraged to _________ the design competition for robots at the university.
Is _______ some German friends visited last week?
-- We are going to hold a sports meeting tomorrow.-- __________ it rains?
She was scared _______ when hearing the sound of explosion.