The correct answer is B. Joule.
A joule (J) is the International System of Units (SI) unit of energy, work, and heat. It is equal to the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
An erg is a unit of energy or work in the CGS system of units. It is equal to the work done by a force of one dyne acting through a distance of one centimeter.
A newton (N) is the SI unit of force. It is equal to the force that, when applied to a mass of one kilogram, produces an acceleration of one metre per second squared.
A dyne is a unit of force in the CGS system of units. It is equal to the force that, when applied to a mass of one gram, produces an acceleration of one centimetre per second squared.
In conclusion, the practical unit of work is the joule.