Because of diesel . . . . . . . . many garages are introducing rationing.

The correct answer is: shortage.

A shortage is a lack of something that is needed. In this case, the garages are rationing diesel because there is a shortage of it. This could be due to a number of factors, such as a decrease in production, an increase in demand, or a disruption in the supply chain.

The other options are incorrect because they do not accurately describe the situation. A deficit is an amount that is less than what is needed or expected. A lack is a state of being without something that is needed or desired. Scarce is something that is not plentiful or abundant.

In conclusion, the correct answer is: shortage.