ANS:A - pycnometer

Pycnometer should be used for coarse grained soil. For fine grand soil if pycnometer is used then kerosin is used instead of water. Because kerosin has good wetting properties. Pycnometer method is more suitable for coarsely grained soil rather than fine grained. Because entrapped air in soil mass can be easily removed in case of coarse grained soil. Here we have to calculate water from soil not from the coarse aggregate. Just because of that we have to use the pycnometer method.

If we use oven dry method then it will also remove the water from coarse aggregates too. But for pycnometer test, specific gravity should be known.

Also I think oven dry test will ever give any error for any kind of soil.