—Stay a bit longer,please. It's been such ________fun having you here.—Thank you,but I've got ________early start tomorrow morning.
Thank you very much for the trouble you have taken _________ me with my English.
Before the conference, a new problem came up __________ could speak on behalf of our group.
He dressed up and went to the party as if ___________.
Scientist are not sure about the ___________ of water on the Mars.
Don’t push me! __________ you know the truth right away?