The correct answer is A. elastic.
Demand is elastic when a small change in price leads to a large change in quantity demanded. In the case of safety pins, a small increase in price would lead to a large decrease in the quantity demanded, as people would find other ways to fasten their clothes or would simply go without safety pins altogether.
Demand is inelastic when a small change in price leads to a small change in quantity demanded. In the case of essential goods like food and water, a small increase in price would not lead to a large decrease in the quantity demanded, as people would still need to buy these goods in order to survive.
Demand is unity when a change in price leads to an equal change in quantity demanded. This is a theoretical concept that does not occur in reality.
In conclusion, the demand for safety pins is elastic. This means that a small change in price leads to a large change in quantity demanded.