The correct answer is A. 0.83.
The specific gravity of a substance is its density relative to the density of water. The density of water is 1 g/cm3. The volume of the wood is 5/0.6 = 8.33 cm3. The mass of the wood is 5 kg. The density of the wood is 5/8.33 = 0.60 g/cm3. The specific gravity of the wood is 0.60/1 = 0.60.
Option B is incorrect because the specific gravity of wood is not 0.6. Option C is incorrect because the specific gravity of wood is not 0.4. Option D is incorrect because the specific gravity of wood is not 0.3.
The specific gravity of a substance is a dimensionless number that is equal to the ratio of the density of the substance to the density of a reference substance. The reference substance is usually water, and the specific gravity of water is 1. The specific gravity of a substance can be used to determine whether the substance will float or sink in water. If the specific gravity of a substance is less than 1, the substance will float in water. If the specific gravity of a substance is greater than 1, the substance will sink in water.