The correct answer is: B. Tight
A double-tuned circuit is a type of resonant circuit that uses two tuned circuits in parallel. The two tuned circuits are coupled together, which means that they share some of the current that flows through them. The amount of coupling between the two tuned circuits is determined by the value of the coupling capacitor.
A tight coupling means that the two tuned circuits are very strongly coupled together. This means that they share a lot of the current that flows through them. This results in a circuit that has a high degree of selectivity. Selectivity is the ability of a circuit to reject signals that are not at the desired frequency. A high degree of selectivity is important for applications such as radio receivers, where it is important to be able to receive only the desired signal and reject all other signals.
A loose coupling means that the two tuned circuits are not very strongly coupled together. This means that they do not share much of the current that flows through them. This results in a circuit that has a lower degree of selectivity.
A critical coupling is a special case of tight coupling. In a critical-coupled circuit, the two tuned circuits are coupled together in such a way that they share exactly half of the current that flows through them. This results in a circuit that has the maximum possible selectivity.
In conclusion, if a high degree of selectivity is desired, then a double-tuned circuit should have tight coupling.