Fill the blanks with the prepositions by, with, or by means

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.