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.