单项选择(每题1分)She opened the window, _____ in some fresh air.
Many sailors think that a thick fog is their ________ enemy.
I made a suggestion ________ he ________ to Australia for further education.
—Will you ________ our house while we are out on holiday? —Well, that ought to be no problem.
The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.
________ the little boy looked after his sick uncle a whole year moved us all.