The correct answer is D. Diamond cannot be used as a lubricant.
Diamond is a very hard material, and it is used as an abrasive for sharpening hard tools. It is also used in jewelry and other decorative items. However, diamond is not a good lubricant because it is too hard and does not have the necessary properties to reduce friction.
Option A is true because each carbon atom in diamond is linked to four other carbon atoms. This forms a three-dimensional network structure that makes diamond very strong and hard.
Option B is also true because diamond is a three-dimensional network structure of carbon atoms. This structure is what gives diamond its strength and hardness.
Option C is also true because diamond is used as an abrasive for sharpening hard tools. The hardness of diamond makes it ideal for this purpose.