No one has been able to satisfactorily explain how or .......... the Moon sporadically sparks.

Experiments in the sonic imaging of moving objects .......... in both the United States and Europe well before the Second World War.

On Mercator's maps, the far northern and southern polar regions are______________.

The earth spins on its axis and _________23 hours, 56 minutes and 4.09 seconds for one complete rotation.

On the slope of Long’s Peak in Colorado ……. The ruin of a gigantic tree.

Antonio Gaudi, architect of Barcelona's Holy Family Church, died before _________ the structure.

Employers often require that candidates have not only a degree, ________________.

Not only knowledge and skills, but also attitudes _________ in school for student's future adjustment to society.