To enjoy the scenery, Sally would spend long hours on the train __________ travel by air.
—May I smoke here?—If you _______, choose a seat in the smoking section.
—Can we ski on this mountain?—Of course.However, at no time _______ you do so alone.
He _______ have completed his work;otherwise, he wouldn’t be enjoying himself by the seaside.
He must have been late for the conference yesterday, _______?
He _______ more visits to his parents.He has been regretting not doing so since they passed away.