Fill the blanks with the prepositions by, with, or by means of Sometimes more than one answer is possible.

1. The lumber was transported ____on_____ train.
2. Current can be varied in a circuit ___________ a rheostat.
3. Earthquakes arc usually caused ___________ the movement of the continental plates.
4. The age of the sample was determined ___________ the carbon 14 dating method.
5. Steel surfaces can be protected ___________ a thin coating of machine oil.
6. The colours of aurora borealis are generated ___________ the effect of solar particles on the various atmospheric gases.
7. The primitive cooling earth was darkened for centuries ___________ hot, dense clouds.
8. The direction of growth of a plant is controlled ___________ light (phototropism).
9. The body temperature of a higher mammal is regulated ___________ the hypothalamus.